BMSAT > Forces > Flashcards

Forces Flashcards

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1
Q

What is a scalar quantity and give an example

A

A quantity that has a magnitude but no direction

  • speed
  • distance
  • temperature
  • mass
  • time
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2
Q

What is a vector quantity and give an example?

A

A quantity that has both magnitude and direction

  • velocity
  • displacement
  • force
  • acceleration
  • momentum
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3
Q

What is a force?

A

A push or pull on an object caused by it interacting with something

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4
Q

What are the two categories of forces and give an example for each

A

Contact
- friction
- tension
- air resistance
- normal contact force

Non contact
- electrostatic
- Gravitational
- Magnetic

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5
Q

Define weight and give the equation

A

Weight = force that acts on an object due to gravity

W =mg
Weight = mass x gravitational field strength

Weight and mass are directly proportional

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6
Q

What is the centre of mass?

A

Point at which an objects weight appears to act

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7
Q

What is a free body diagram?

A

Shows all the forces acting on an isolated object

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8
Q

What is an equilibrium?

A

When the forces acting on an object are balanced and the resultant force is zero

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9
Q

What is the resultant force?

A

A single force that can replace all the forces acting on an object to give the same effect as all the original forces acting together

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10
Q

What is work done and what is the equation for it?

A

When a force moves an object, energy is transferred and work is done.

W = Fs
Work done = force x distance

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11
Q

What are the two types of deformation?

A

Elastic - object goes back to its original shape and length after forces have been removed

Inelastic - object doesn’t go back to its original length and shape after forces have been removed

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12
Q

What is the equation for force and extension?

A

F = ke
Force = spring constant x extension

Extension is directly proportional to force

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13
Q

What is the limit of proportionality

A

When force gets too big and exceeds the limit of proportionality, force and extension are no longer directly proportional - curve levels off

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14
Q

Why must more than one force be applied to an object to change its shape?

A

When only one force is applied it caused the stationary object to move and accelerate, not change shape.

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15
Q

What happens to the elastic potential energy store in elastic deformation?

A

Force is applied causing a stretch or compress
Work is done
All energy is transferred to elastic potential energy store.

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16
Q

What is a moment and give its equation?

A

The turning effect of a force

M = Fd
Moment = force x perpendicular distance from pivot

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17
Q

What is a balanced moment?

A

When the total clockwise moment and anticlockwise moment are balanced.

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18
Q

What are gears used for?

A

Transmit the rotational effect of a force from one place to another

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19
Q

What do levers do and how?

A

Levers make it easier to do work.

Increase the distance between pivot and force
Less force is required to get the same moment
Easier to lift load

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20
Q

What is the equation for pressure?

A

P = F/a
Pressure = force / area

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21
Q

How do gears work?

A

Gears have interlocking teeth
When one gear turns the other is forced to turn in the opposite direction
Large gears have larger moments but turn slower

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22
Q

What is a fluid?

A

A liquid or gas

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23
Q

How to calculate pressure in a column?

A

Pressure = height of column x density x gravitational field strength

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24
Q

What is upthrust?

A

The resultant force acting upwards on an object submerged in liquid due to the pressure being greater at the bottom of the object.

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25
What is the atmosphere?
A thin layer of air that surrounds the earth
26
How is atmospheric pressure created?
Created when air molecules collide with a surface
27
What factors affect whether and object sinks or floats?
If the upthrust = weight the object floats - less dense than liquid If the weight is greater than upthrust than the objects sinks - denser than liquid
28
How does atmospheric pressure decrease?
Height increases Number of air molecules and weight of air decreases (less dense atmosphere) Pressure decreases
29
What is the distance?
How far an object has moved (Scalar)
30
What is displacement?
The distance and the direction in a straight line from an objects starting point to its finishing point (Vector)
31
What is speed and its equation?
How fast youre going (scalar - no regard for direction) S = vt Distance = speed x time
32
What is velocity?
Speed in a certain direction (vector)
33
What is the typical speed of humans and transport in M/s?
Walking - 1.5 Running - 3 Cycling - 6 Car - 25 Train - 30 Plane - 250
34
What is the speed of sound in air?
330 m/s
35
What is the velocity and speed like of an object in circular motion?
An object in circular motion has a constant speed and is always changing direction therefore the velocity is changing.
36
What is acceleration and its equation?
The change in velocity in a certain amount of time Acceleration = change in velocity/time
37
What is peoples running, walking and cycling speed affected by?
- ability - age - distance travelled - type of ground
38
What are the characteristics of a distance time graph?
For an object moving in a straight line - Straight uphill section - steady speed Flat section - stopped Steepening curve = acceleration Curve levels off - deceleration Gradient = speed
39
What are the characteristics of a velocity time graph?
Straight uphill - constant acceleration Flat sections - steady speed Steepening curve - increasing acceleration Straight downhill - constant deceleration Gradient - acceleration Area under graph = distance travelled
40
What is Newton’s first law
Law of inertia A stationary object remains stationary and an object in constant motion remains in constant motion in the same direction until an unbalanced force acts upon it.
41
What is inertia?
The tendency of an object to continue in the same state of motion
42
What is Newton’s second law?
F = ma Force = mass x acceleration Force is directly proportional to acceleration Acceleration is inversely proportional to mass
43
What is inertial mass?
The measure of how hard it is the change an objects velocity M = F/a
44
What is Newton’s third law?
Two interacting objects exert equal and opposite forces on each other
45
What is friction?
A force that acts to oppose an objects motion. It always acts in the opposite direction to movement
46
What is drag?
The frictional force caused by any fluid on a moving object e.g air resistance
47
How is terminal velocity reached?
Force of gravity is greater than frictional force Object accelerates Speed increases so friction increases Frictional force then is equal to gravity Resultant force is zero Terminal velocity is reached
48
What can lower the terminal velocity and why?
A parachute because it increases air resistance
49
What is the typical reaction time?
0.2 and 0.9s
50
What three factors can affect reaction time?
- tiredness - drugs - alcohol
51
Describe the ruler drop test
Get someone to hold ruler between your thumb and forefinger Let them drop ruler unexpectedly Catch the ruler with your thumb and forefinger as quick as possible Measure the distance the ruler dropped and calculate reaction time The longer the distance the longer the reaction time.
52
How do you calculate stopping distance?
Stopping distance = thinking distance + braking distance
53
What are two factors that increase thinking distance?
- faster vehicle speed - slower reaction time
54
What are the four factors increasing breaking distance?
- faster vehicle speed - poor road surface - wet or icy weather - damaged/worn brakes and tires
55
What happens to thinking distance and breaking distance when speed doubles?
If speed doubles - thinking distance doubles - breaking distances quadruples
56
What happens to the breaks when stopping?
Break pads are pressed into the wheels Causing friction which in turn causes work to be done Energy is transferred from kinetic energy stores to thermal energy stores Breaks heat up Large deceleration may cause the breaks to overheat and may cause loss of control
57
What is the equation for momentum?
P = mv Momentum = mass x velocity Kg m/s = kg x m/s The greater the mass/velocity, the greater the momentum
58
What is the conservation of momentum?
In a closed system the total momentum before an event is equal to the momentum after an event
59
What is the resultant force equal to and what does it mean?
The rate of change in momentum Increases the time taken for momentum to change which decreases the force acting on an object
60
What five safety features increase time for change in momentum?
- air bags - seat belts - cushioned playground flooring - crash mats - bike helmets
61
How do air bags work?
Air bags inflate during a car crash Compressing the air decreases velocity over time as opposed to hitting the dashboard Rate of change of momentum is smaller Forces felt are smaller
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