1
Q
What is a force?
A
A force is a push or a pull on an object.
2
Q
What unit is used to measure force?
A
The unit in which we measure force is a newton (N).
3
Q
Who is the newton named after?
A
The newton is named after Sir Isaac Newton, an English physicist and mathematician.
4
Q
What is the definition of a newton?
A
The Newton is defined as the force needed to accelerate 1 kilogram of mass at 1 metre per second squared (m/s²).
5
Q
What effect can a force have on an object?
A
A force can cause an object to move, stop, or change direction.
6
Q
Do forces have to be between objects which are touching?
A
No, forces can act at a distance without direct contact.
7
Q
Who is recognized as one of the most influential scientists of all time?
A
Sir Isaac Newton is recognized as one of the most influential scientists of all time.
8
Q
What are the dates of Sir Isaac Newton’s life?
A
Sir Isaac Newton lived from 25 December 1642 to 20 March 1727.
9
Q
What do we use every day of our lives?
A
We use forces every day of our lives.
10
Q
How do our bodies rely on forces?
A
Our muscles pull on our bones to allow us to move.
11
Q
What do our feet do when we walk?
A
Our feet push on the ground when we walk.
12
Q
What activities involve forces?
A
To open doors, to pick up our food - everything we do involves some kind of force.
13
Q
What can we do to learn about forces?
A
Let’s experiment with forces and see what we can do.
14
Q
What is deformation?
A
Deformation is the change in shape of an object due to forces acting on it.
15
Q
What effects can forces have on an object?
A
Forces can change the shape, motion, and direction of an object.
16
Q
What is velocity?
A
Velocity is the rate of change of the position of an object, including both speed and direction.
17
Q
How does speed differ from velocity?
A
Speed describes how fast an object is moving, while velocity includes both speed and direction.
18
Q
What is constant velocity?
A
Constant velocity means an object travels at the same speed in the same direction.
19
Q
What is acceleration?
A
Acceleration is the rate of change of a body’s velocity with time.
20
Q
How can an object’s motion be changed?
A
An object’s motion can be changed by applying a force to make it speed up or slow down.
21
Q
What does Newton’s Third Law of Motion state?
A
When one body exerts a force on a second body, the second body simultaneously exerts a force equal in strength and opposite in direction to that of the first body.
22
Q
What happens when one object exerts a force on another object?
A
The second object exerts a force back on the first object.
23
Q
What are the two forces described in Newton’s Third Law?
A
The action and the reaction.
24
Q
How do forces act according to Newton’s Third Law?
A
Forces act in pairs on different objects.
25
What is experienced when you push against a wall?
You experience the wall exerting a force back on you.
26
What is the relationship between the force exerted by the second object and the first force?
The force exerted by the second object is equal in strength and opposite in direction to the first force.
27
What happens when more than one force acts on an object?
The forces combine to make a net (overall) force.
28
What is the net force when two equal and opposite forces act on an object?
The net force is 0 N.
29
What occurs when one force is greater than another?
The net force is greater than 0 N, resulting in a resultant force.
30
What happens in a tug-of-war when forces are equal?
The rope remains stationary.
31
What happens in a tug-of-war when one group exerts a larger force?
The rope will move in the direction of the larger force.
32
What occurs when two forces act in the same direction?
They add together to produce a larger overall net force.
33
How do we represent forces in a diagram?
We use arrows to represent the forces acting from the center of the object.
34
What is the purpose of the simulation mentioned?
To discover more online as you interact with the simulation on forces and motion.
35
Why is the force exerted by Viantha given a negative value?
Because it is in the opposite direction to the force exerted by Jabu.
36
What does the direction of the arrow in a force diagram indicate?
The direction in which the force is acting.
37
What does the length of the arrow in a force diagram indicate?
The size of the force; a small force is shown with a short arrow, and a large force with a long arrow.
38
Can more than one force act on an object at the same time?
Yes, more than one force can act on an object simultaneously.
39
What determines the effect of different forces acting together?
The size of each force and the direction in which each force is acting.
40
How can we represent the forces acting on Rod?
Using a circle to represent Rod and different length arrows to represent the forces acting on him, known as a free-body diagram.
41
What is the net force acting on Rod when Jabu pulls with 10 N and Viantha pulls with 6 N?
The net force is calculated as follows: net force = 10 N + (- 6 N) = 4 N to the left.
42
What happens to the net force if all forces act in the same direction?
The net force is the sum of the different forces.
43
What happens when two forces act in the same direction on an object?
They are added together to produce a net force, which is the sum of the two smaller forces.
44
What is Hooke's Law?
Hooke's Law states that when a force stretches or compresses a spring, the distance that the spring moves from its rest position is directly proportional to the size of the force.
45
How do we measure a force?
We use an instrument called a spring balance.
46
What is a spring balance?
A spring balance is a simple device consisting of a spring which, when stretched, gives a reading of the force used to stretch the spring.
47
Do we always have to be in contact with an object to exert a force?
No, we do not always have to be in contact with an object in order to exert a force.
48
What is friction?
Friction is the force which opposes motion. It always acts in the opposite direction to the motion of the object.
49
What is normal force?
Normal force is the support force exerted upon an object that is in contact with another stable object.
50
What is tension?
Tension is the force that is transmitted through a string, rope, or wire when it is pulled tight by forces acting from opposite ends.
51
What is compression?
Compression is the force that results from pushing or pulling an object, causing it to become smaller or denser.
52
What are contact forces?
Contact forces are forces between objects which are touching each other.
53
What are non-contact (field) forces?
Non-contact forces are forces exerted by objects that are not in contact with each other.
54
What happens when you kick a ball across the grass?
The ball moves quickly at first but then slows down due to the force of friction acting on it.
55
How does friction affect motion?
Friction resists movement when the object and surface are in contact, acting in the opposite direction to the object's motion.
56
What direction does friction act on a ball that has just been kicked?
Friction acts in the opposite direction to the motion of the ball.
57
What factors affect the amount of force required to move objects?
The amount of force required depends on all the forces acting on the object.
58
What forces were shown acting on the go-cart?
The forces of two learners pushing on the go-cart were shown.
59
What other forces act on the go-cart as it moves?
Friction and weight are also acting on the go-cart.
60
What causes an object on Earth to have weight?
An object has weight due to the gravitational force of attraction of the Earth.
61
What will be learned in the next section?
We will learn more about weight and the gravitational force.
62
What is the normal force?
The normal force is a contact force that acts perpendicularly to the surface an object is resting on.
63
How does the normal force relate to weight on a level surface?
On a flat, level surface, the normal force is equal to the weight of the object but in the opposite direction.
64
What is the relationship between normal force and friction?
There is a relationship between the friction that a body experiences and the normal force.
65
What is the purpose of the simulation mentioned?
The simulation allows you to explore the forces at work when trying to push a filing cabinet.
66
What does the free-body diagram of the go-cart include?
The free-body diagram includes the normal force, friction, and weight.
67
What causes a material to heat up and melt?
Friction causes a material to heat up and melt. When two objects are rubbed together, they heat up until one reaches the melting temperature.
68
What happens when a material reaches its melting temperature?
Particles break free as the material melts away.
69
What factors affect the force of friction?
The force of friction depends on the type of surface and the normal force.
70
What must be applied to move an object against friction?
A force greater than the frictional force needs to be applied to overcome the friction.
71
What is an example of friction in action?
Pushing a friend in a go-cart demonstrates friction between the go-cart and the ground.
## Footnote
If two forces of 7N and 10N are pushing the go-cart forward and the friction is 5N, the net force can be calculated.
72
What is the advantage of friction?
Friction enables movement and prevents slipping, such as the friction between our feet and the ground.
73
How does friction help vehicles?
Friction helps keep cars from skidding as the tyres experience friction between the tread and the roadway.
74
What is tension?
Tension is a contact force that exists in a rope when it is pulled tight.
75
How does tension work in a pulling scenario?
When a person pulls on a rope, the rope pulls a block, creating tension in the rope.
76
What is compression?
Compression is a force that acts to deform or squash an object.
77
Can you give an example of compression?
Crushing a ball of dough with your fingers exerts a compression force on the dough.
## Footnote
The dough changes shape and deforms.
78
What is another example of compression?
Crushing a tennis ball or a cooldrink can between the palms of your hands.
79
What are tension forces?
Tension forces are two forces acting on one object in opposite directions (away from each other) to stretch the object.
80
What are compression forces?
Compression forces are two forces acting on one object in opposite directions (towards each other) to compress or deform the object.
81
What is an example of compression and tension in everyday life?
A bridge experiences both compression and tension due to the weight of the cars and other vehicles which pass over it.
82
What are field forces?
Field forces are non-contact forces that act over a distance and do not require objects to be touching.
83
What is a field?
A field is a region in space where an object (with certain properties) will experience a force.
84
What types of forces have been discussed?
We have been looking at contact forces, which include friction, normal forces, compression, and tension.
85
What are the most common examples of fields?
The most common examples of fields are: gravitational field, magnetic field, electric field.
86
What are field forces better described as?
With field forces, it is better to talk about repulsion and attraction.
87
What causes things to fall down towards the Earth?
The force which causes things to fall down towards the Earth is the gravitational force.
88
What type of force is gravitational force?
Gravitational force is a force of attraction (pull) between any two objects with mass.
89
What does the Earth exert a gravitational pull on?
The Earth exerts a gravitational pull on you, the desks in your classroom, and the chairs in your classroom.
90
Why do objects fall to the ground?
Objects fall to the ground because the Earth's gravitational force pulls everything down towards its center.
91
Do you exert a gravitational pull on the Earth?
Yes, you, your desk, your chair, and falling objects exert an equal but opposite pull on the Earth.
92
Why doesn't the Earth's movement change noticeably due to gravitational forces?
The forces on the Earth do not cause it to move noticeably due to its massive size.
93
Who developed the Law of Universal Gravitation?
Newton developed his Law of Universal Gravitation in 1687.
94
What inspired Newton's work on gravitation?
Newton's work may have been inspired by watching an apple fall from a tree.
95
How is gravity measured?
Gravity is a force and is therefore measured in Newtons.
96
What direction do the arrows show in the gravitational field of the Earth?
The arrows point towards the center of the Earth because the gravitational force is always attractive.
97
What are the most common examples of fields?
The most common examples of fields are: gravitational field, magnetic field, electric field.
98
What are field forces better described as?
With field forces, it is better to talk about repulsion and attraction.
99
What causes things to fall down towards the Earth?
The force which causes things to fall down towards the Earth is the gravitational force.
100
What type of force is gravitational force?
Gravitational force is a force of attraction (pull) between any two objects with mass.
101
What does the Earth exert a gravitational pull on?
The Earth exerts a gravitational pull on you, the desks in your classroom, and the chairs in your classroom.
102
Why do objects fall to the ground?
Objects fall to the ground because the Earth's gravitational force pulls everything down towards its center.
103
Do you exert a gravitational pull on the Earth?
Yes, you, your desk, your chair, and falling objects exert an equal but opposite pull on the Earth.
104
Why doesn't the Earth's movement change noticeably due to gravitational forces?
The forces on the Earth do not cause it to move noticeably due to its massive size.
105
Who developed the Law of Universal Gravitation?
Newton developed his Law of Universal Gravitation in 1687.
106
What inspired Newton's work on gravitation?
Newton's work may have been inspired by watching an apple fall from a tree.
107
How is gravity measured?
Gravity is a force and is therefore measured in Newtons.
108
What direction do the arrows show in the gravitational field of the Earth?
The arrows point towards the center of the Earth because the gravitational force is always attractive.
109
What can you interact with to see the relationship between gravity, mass, and distance?
A simulation that illustrates the relationship between gravity and the masses of objects and the distance between them.
## Footnote
Visit: bit.ly/l6PDe2w
110
What happens when you move the Sun, Earth, Moon, and space station in a simulation?
You can observe how it affects their gravitational forces and orbital paths.
## Footnote
Visit: bit.ly/199wWdE
111
What can you build with a simulation related to the solar system?
You can build your own solar system and experiment with the masses and orbits.
## Footnote
Visit: bit.ly/1hYfnzd
112
Why are we attracted downwards towards the center of the Earth?
Because the Earth has a large mass, creating a gravitational pull towards it.
113
What happens when two small objects are compared to larger objects in terms of gravity?
Two small objects have a very weak gravitational attraction, while larger objects, like the Moon and Earth, have a much greater gravitational force.
114
What holds the planets in orbit around the Sun?
The gravitational force of attraction between the Sun and the planets.
115
What is the relationship between the Sun and the planets in our solar system?
There is a gravitational force of attraction between the Sun and planets, and between planets and their moons.
116
What affects the gravitational force of attraction between objects?
The distance between them. The further objects are away from each other, the smaller the gravitational force.
117
What holds all components in our Universe together?
A gravitational force.
118
What is the relationship between the mass of objects and gravitational force?
The greater the mass of the objects, the stronger the gravitational force of attraction between them.
119
How does proximity affect gravitational force?
The closer objects are to each other, the stronger the gravitational force between them.
120
What is the definition of mass?
The amount of matter in an object, indicating how many particles it contains.
## Footnote
Mass is measured in kilograms (kg) and is independent of location.
121
In what units is mass measured?
Kilograms (kg)
## Footnote
Mass remains constant regardless of the location of measurement.
122
What does the mass of an object tell us?
How many atoms are in the object.
## Footnote
This relates to the concept of particles in Matter and Materials.
123
How does weight differ from mass?
Weight depends on both the mass of the object and the strength of the gravitational force acting on it.
## Footnote
This means weight can change based on location.
124
What is the unit of measurement for weight?
Newtons (N)
## Footnote
Weight is the gravitational force exerted on an object.
125
What happens to the weight of an object when measured on different planets?
It changes depending on the strength of the gravitational force.
## Footnote
For example, a wooden block's weight will differ on Earth compared to the Moon.
126
True or False: The weight of an object is the same everywhere.
False
## Footnote
Weight varies with gravitational force, unlike mass.
127
Fill in the blank: The word mass comes from the Greek word _______.
maza
## Footnote
Maza translates to a lump of dough or cake.
128
What common misconception do people have about weight?
People often confuse weight with mass, stating changes in weight without considering gravitational effects.
## Footnote
For example, saying 'I gained weight' without context.
129
What is weight?
Weight is the force of gravity pulling you towards the centre of the Earth. It is measured in newtons.
130
What is gravitational acceleration on Earth?
On Earth, gravitational acceleration is 9.8 m/s².
131
How is weight calculated?
Weight (W) is calculated by multiplying an object's mass (m) by the gravitational acceleration (g): W = m x g.
132
What happens to objects in free-fall?
Objects are in free-fall when the only force acting on them is the gravitational force.
133
How does weight change on the Moon?
On the Moon, you would weigh one-sixth of what you do on Earth because the Moon's gravity is one-sixth that of Earth's.
134
How does weight change on Jupiter?
On Jupiter, you would weigh 2.5 times more than you do on Earth because Jupiter's gravity is 2.5 times that of Earth's.
135
Does mass change on different celestial bodies?
Your actual mass would stay the same regardless of whether you are on the Moon or Jupiter.
136
What is the mass of the Earth?
The mass of the Earth is 5.972 × 10²⁴ kg.
137
What remains the same for an astronaut regardless of location?
An astronaut's mass remains the same wherever it is measured.
138
What does an astronaut's weight depend on?
An astronaut's weight depends on where you measure it.
139
What is the weight of an astronaut on Earth?
An astronaut weighs 1200 N on Earth.
140
What is the weight of an astronaut on the Moon?
An astronaut weighs 200 N on the Moon.
141
How do you calculate weight on Earth?
Weight on Earth is calculated as mass multiplied by gravitational acceleration: 60 kg x 9.8 m/s² = 588 N.
142
How do you calculate weight on the Moon?
Weight on the Moon is calculated as mass multiplied by gravitational acceleration: 60 kg x 1.6 m/s² = 96 N.
143
What does a bathroom scale measure?
A bathroom scale actually measures weight and converts it to mass.
144
What did Felix Baumgartner experience during his freefall?
He experienced free-fall or weightlessness.
145
What is the weight of a person?
The weight of a person is the force of gravitational attraction to the Earth that person experiences.
146
Do astronauts lose their weight in free-fall?
No, they feel weightless but have not lost their weight; they still experience the Earth's gravitational attraction.
147
Why do astronauts appear to float?
They appear to float because they are in free-fall with their moving spacecraft, both falling at the same rate.
148
What are magnets?
Certain materials that have strong magnetic fields around them.
149
What are the two poles of a magnet?
A north pole and a south pole.
150
What are materials that are strongly attracted to magnets called?
They are said to be magnetic.
151
What do magnets exert on other magnets and magnetic materials?
Magnets exert forces.
152
What are magnetic materials?
Magnetic materials are those metals that are attracted to magnets.
153
Which metals are considered magnetic materials?
The magnetic materials are iron, nickel, and cobalt.
154
Can alloys be magnetic?
Yes, alloys that include any magnetic materials can also be attracted to magnets.
155
Is steel attracted to magnets?
Yes, steel is an alloy that contains iron, so it can be attracted to a magnet.
156
Can magnetic forces act over a distance?
Yes, magnetic forces can act over a distance.
157
Do magnetic forces still act if there is something in the way?
This is a question to explore further.
158
What is the magnetic force field?
The magnetic force field is the space around a magnet in which it can attract or repel another magnet.
159
How does the magnetic field appear in terms of dimensions?
The magnetic field is actually all around the magnet, in three dimensions.
160
What are field lines?
Field lines are used to represent the magnetic force field, showing something we can't actually see.
161
What does the density of field lines indicate?
The closer the field lines are drawn together, the stronger the field being described.
162
What direction do field lines go?
Field lines go from the north pole to the south pole.
163
What happens between opposite poles of magnets?
Opposite poles attract.
164
What is the visual representation of magnetic field lines?
The pattern of field lines can be represented in diagrams, showing the interaction between magnets.
165
What is the Earth's magnetic field compared to?
The Earth is like a bar magnet with a North and a South Pole.
166
What are the Southern lights called?
The Southern lights are also called the Aurora Australis.
167
What are the Northern lights called?
The Northern lights are called the Aurora Borealis.
168
What happens to like poles?
Like poles repel.
169
Where is the Earth's magnetic field strongest?
A field is strongest next to the magnet and gets weaker further away from the magnet.
170
What is the theory behind Earth's magnetic field?
The theory is that the superhot liquid iron in the Earth's core moves in a rotational pattern, leading to weak magnetic forces around the Earth's rotation.
171
What is the function of a compass?
A compass is used to tell direction.
172
How does a plotting compass work?
A plotting compass has a needle with a small magnet that points to magnetic north because it is attracted to the opposite magnetic field.
173
What does the needle of a compass point to?
The needle points to magnetic north.
174
What are the Southern and Northern Lights?
They are natural light displays caused by charged particles from the Sun interacting with Earth's atmosphere.
175
How do charged particles from the Sun reach Earth?
Charged particles escape from the Sun's surface and move outward in all directions until they reach Earth.
176
What happens to charged particles when they reach Earth?
Some are trapped by Earth's magnetic field in areas called belts.
177
What occurs when charged particles escape the belts?
They spiral along the magnetic field lines towards the magnetic poles and enter Earth's atmosphere.
178
What do charged particles do when they enter Earth's atmosphere?
They interact with atmospheric gas particles, causing beautiful light shows.
179
What are ferrofluids?
Ferrofluids are liquids that can become magnetised in the presence of a strong magnetic field.
180
Can you provide an example of a ferrofluid?
An example of a ferrofluid is a liquid that can become magnetised in a magnetic field.
181
What are the Southern and Northern Lights?
They are natural light displays caused by charged particles from the Sun interacting with Earth's atmosphere.
182
How do charged particles from the Sun reach Earth?
Charged particles escape from the Sun's surface and move outward in all directions until they reach Earth.
183
What happens to charged particles when they reach Earth?
Some are trapped by Earth's magnetic field in areas called belts.
184
What occurs when charged particles escape the belts?
They spiral along the magnetic field lines towards the magnetic poles and enter Earth's atmosphere.
185
What do charged particles do when they enter Earth's atmosphere?
They interact with atmospheric gas particles, causing beautiful light shows.
186
What are ferrofluids?
Ferrofluids are liquids that can become magnetised in the presence of a strong magnetic field.
187
Can you provide an example of a ferrofluid?
An example of a ferrofluid is a liquid that can become magnetised in a magnetic field.
188
What is the type of charge on a proton?
Positive charge
189
What is the type of charge on an electron?
Negative charge
190
What is the charge on a neutron?
Neutral charge
191
How are atoms normally charged?
Atoms are normally neutral because they contain the same number of protons and electrons.
192
What happens when two surfaces are rubbed together?
Electrons can be transferred from one object to another due to friction.
193
Can protons be transferred between atoms?
No, protons are fixed in place in the nucleus and cannot be transferred.
194
Which electrons move during the rubbing process?
Only the outer electrons move.
195
What happens when an object has more electrons than protons?
The object is negatively charged.
196
What happens when an object has fewer electrons than protons?
The object is positively charged.
197
What is the overall charge when there are 6 positive charges and 6 negative charges?
There is zero overall charge. The object is neutral.
198
What is the overall charge when there are 8 positive charges and 6 negative charges?
The overall charge is +2. The object is positively charged.
199
What is the overall charge when there are 6 positive charges and 9 negative charges?
The overall charge is -3. The object is negatively charged.
200
What occurs as a result of friction between objects?
The transfer of electrons takes place.
201
What happens when oppositely charged objects are brought together?
Let's look at the effects of this interaction.
202
What happens when perspex rods are rubbed with cloth?
Electrons are transferred from the perspex to the cloth, resulting in both perspex rods having the same charge.
## Footnote
Objects with the same charge repel each other, creating an electrostatic force of repulsion.
203
What charge does the plastic rod have after being rubbed with cloth?
Electrons are transferred from the cloth to the plastic rod, giving the plastic rod an opposite charge to the perspex rod.
## Footnote
Objects with different charges attract each other, creating an electrostatic force of attraction.
204
How does distance affect electrostatic force?
The strength of the electrostatic force increases as the distance between charged objects decreases.
205
What is the behavior of two negatively charged objects?
They will repel each other.
206
What is the behavior of two positively charged objects?
They will repel each other.
207
What happens when a positively charged object is brought closer to a negatively charged object?
They will attract each other.
208
What is the source of lightning?
Lightning is a demonstration of an electrostatic spark.
209
What is a Van de Graaff generator used for?
The Van de Graaff generator can be used to demonstrate the effects of an electrostatic charge.
210
What happens when the Van de Graaff generator is turned on?
The big metal dome at the top becomes positively charged.
211
How can the charge on the Van de Graaff generator be discharged?
The charge can be discharged by bringing another insulated metal sphere close to the dome.
212
What occurs when the insulated metal sphere is brought close to the charged dome?
Electrons will jump to the dome from the metal sphere and cause a spark.
213
How does a spark from a Van de Graaff generator relate to lightning?
A spark is a small electrostatic discharge, while lightning is a huge electrostatic discharge.
214
What causes clouds to become charged during a lightning storm?
Friction between the clouds and the moisture in the clouds causes the clouds to become charged.
215
What is the charge distribution in a cloud during a lightning storm?
The bottom of the clouds becomes negatively charged and the top becomes positively charged.
216
What happens when the build-up of charge in a cloud becomes too large?
Electrons move from the bottom of the cloud to the ground where they are 'earthed'.
217
What results from the massive energy transfer during a lightning strike?
It results in extremely bright light, heat, and sound.
218
What is a lightning flash?
A lightning flash is a massive discharge between charged regions within clouds, or between clouds and the Earth.
219
What causes the thunder-clap heard during a lightning storm?
The thunder-clap is the air moving as a result of electrons moving.
220
Why is lightning extremely dangerous?
If the electrons move through a person on their way to the ground, the large amounts of energy can cause significant damage.
221
What can happen to a person struck by lightning?
A person can suffer serious injury, even death.
222
What is the historical significance of using friction to generate charge?
The fundamental idea dates back to the 17th century, but the generator was invented by Robert Van de Graaff in 1929.
223
Where does South Africa rank in terms of lightning strikes?
South Africa has one of the highest incidences of lightning strikes in the world.
224
What is a Van de Graaff generator used for?
The Van de Graaff generator can be used to demonstrate the effects of an electrostatic charge.
225
What happens when the Van de Graaff generator is turned on?
The big metal dome at the top becomes positively charged.
226
How can the charge on the Van de Graaff generator be discharged?
The charge can be discharged by bringing another insulated metal sphere close to the dome.
227
What occurs when the insulated metal sphere is brought close to the charged dome?
Electrons will jump to the dome from the metal sphere and cause a spark.
228
How does a spark from a Van de Graaff generator relate to lightning?
A spark is a small electrostatic discharge, while lightning is a huge electrostatic discharge.
229
What causes clouds to become charged during a lightning storm?
Friction between the clouds and the moisture in the clouds causes the clouds to become charged.
230
What is the charge distribution in a cloud during a lightning storm?
The bottom of the clouds becomes negatively charged and the top becomes positively charged.
231
What happens when the build-up of charge in a cloud becomes too large?
Electrons move from the bottom of the cloud to the ground where they are 'earthed'.
232
What results from the massive energy transfer during a lightning strike?
It results in extremely bright light, heat, and sound.
233
What is a lightning flash?
A lightning flash is a massive discharge between charged regions within clouds, or between clouds and the Earth.
234
What causes the thunder-clap heard during a lightning storm?
The thunder-clap is the air moving as a result of electrons moving.
235
Why is lightning extremely dangerous?
If the electrons move through a person on their way to the ground, the large amounts of energy can cause significant damage.
236
What can happen to a person struck by lightning?
A person can suffer serious injury, even death.
237
What is the historical significance of using friction to generate charge?
The fundamental idea dates back to the 17th century, but the generator was invented by Robert Van de Graaff in 1929.
238
Where does South Africa rank in terms of lightning strikes?
South Africa has one of the highest incidences of lightning strikes in the world.
239
What precautions should we take during a lightning storm?
The safest place to be in a lightning storm is indoors. Stay away from windows and metal objects.
240
What should you do if you cannot get inside during a lightning storm?
Avoid standing next to tall objects or metal objects.
241
What should you do if you are travelling in a car during a storm?
Stay inside the car until the storm subsides.
242
How is a force defined?
A force is defined as a push or a pull on an object.
243
How are forces measured?
Forces are measured in newtons (N).
244
What can a force change?
A force can change the shape, direction and motion of an object.
245
What is the action and reaction in forces?
The force acting on the object is called the action, and the force that the object exerts back in the opposite direction and equal in magnitude is the reaction.
246
What is the net or resultant force?
The net or resultant force is the sum of all the forces acting on the object.
247
How can forces acting on a body be represented?
Forces acting on a body can be represented as a free-body diagram where the arrows indicate the direction and magnitude of the different forces.
248
What are the two main groups of forces?
The two main groups of forces are contact and non-contact (field) forces.
249
What are contact forces?
Contact forces act when objects are in contact (touching) with each other.
250
What is friction?
Friction is the force opposing motion between two surfaces as they rub against each other.
251
What are compression forces?
Compression forces are two forces acting on one object, moving in opposite directions (towards each other) to compress or deform the object.
252
What are tension forces?
Tension forces are two forces acting on one object, moving in opposite directions (away from each other) to stretch the object.
253
What are non-contact forces?
Non-contact forces can act over a distance and objects do not have to be touching each other.
254
What are common examples of field forces?
Common examples of field forces are magnetic, electrostatic and gravitational forces.
255
What is a field in the context of forces?
A field is a region in space where a certain object with certain properties will experience a force.
256
What is gravitational force?
Gravitational force is a force of attraction between two bodies due to their mass.
257
How does gravitational force change?
The gravitational force increases with mass and decreases with the distance between the bodies.
258
What is weight?
The weight of a body is the gravitational force exerted on an object by the Earth (or Moon or other planet).
259
How does weight vary?
The weight will vary depending on where it is measured.
260
What is mass?
The mass of an object is a measure of how much matter it contains.
261
Does mass change based on location?
The mass stays constant no matter where it is determined.
262
How is weight calculated?
Weight is calculated as W = m x g, where g is the gravitational acceleration.
263
What is the value of g on Earth?
On Earth, g = 9.8 m/s².
264
What is a magnet?
A magnet is a material which has a strong magnetic field around it.
265
What substances exhibit magnetic forces of attraction with a magnet?
Magnetic forces of attraction exist between a magnet and a magnetic substance, such as iron, steel, cobalt, and nickel.
266
What are the two poles of a magnet?
A magnet has two poles, a north and south pole. Opposite poles attract each other and like poles repel each other.
267
How does the Earth relate to magnetism?
The Earth has a magnetic field around it. We can use compasses to tell direction as the needle is a magnet which points to magnetic North.
268
What happens when certain materials are rubbed together?
When certain materials are rubbed together, the friction between them causes electrons to move from one material to the other. The objects then have an electrostatic charge, due to either the loss or gain of electrons.
269
What is a charge?
A charge is a fundamental property of matter. Electrons carry negative charges and protons carry positive charges.
270
What happens to an object that gains or loses electrons?
An object which has gained electrons will be negatively charged. An object which has lost electrons will be positively charged.
271
What is the electrostatic force between charged objects?
There is an electrostatic force of attraction between objects with opposite charges, and repulsion between objects with like charges.
272
How can thunder clouds become charged?
Thunder clouds can become charged as the water and air particles rub against each other. A lightning strike occurs when there is a huge discharge between the thunderclouds and the ground.
273
What precautions should be taken during lightning storms?
Lightning is dangerous and safety precautions should be adhered to during lightning storms.
NS term 3 Grade 9
flashcards
Decks in class (13)
# Cards
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Forces273
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NS demarcation Aug 25117
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Resistance113
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Electric Cells As Energy Systems70
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Series And Parallel Circuits135
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Safety With Electricity And The National Electricity Grid Unit 1419
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Electricity Generation Unit 217
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Nuclear Power In SA Unit 335
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National Electricity Grid Unit 415
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Topic 14 Revision8
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Topic 15 Unit 1 The Cost Of Power Consumption0
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Unit 1 The Cost Of Power Consumption42
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Term 3 Test questions13
