Chapter 3 - Dynamics

Question 1

Define “force”

Answer 1

An influence which changes, or tries to change, the state of motion of a body or the shape or size of a body

Question 2

What is the Sl unit for force?

Answer 2

Newton (N)

Question 3

Define “mass”

Answer 3

A measure of the amount of matter in a body (or object)

Question 4

What is the SI unit for mass?

Answer 4

kilogram (kg)

Question 5

What is used to measure mass?

Answer 5

electronic balance, beam balance

Question 6

Define “gravitational field”

Answer 6

A region in which a mass experiences a force due to gravitational attraction

Question 7

Define “gravitational field strength”

Answer 7

The gravitational force (in N) acting on a unit mass

Question 8

Gravitational field strength is measured in ________

Answer 8

N kg^-1

Question 9

Gravitational acceleration / acceleration due to gravity is measured in ________

Answer 9

m s^-2

Question 10

Formula to calculate weight

Answer 10

W = mg

[ weight (gravitational force) = mass x gravitational acceleration ]

Question 11

Similarity between mass and weight

Answer 11

Both are physical quantities

Question 12

Differences between mass and weight (5)

Answer 12

• Mass is a measure of the amount of substance in a body whereas weight is due to the gravitational force on a body
• Mass is a scalar whereas weight is a vector
• SI unit for mass is kg whereas SI unit for weight is N
• Mass is constant regardless of the gravitational field strength whereas weight varies according to the gravitational field strength
• Mass is usually measured by a beam/electronic balance whereas weight is measured by a spring/compression balance

Question 13

Define “friction”

Answer 13

A force that exists between two surfaces when at least one is rough

Question 15

Friction opposes ________ between two surfaces in contact

Answer 15

relative motion

Question 16

Friction ________ with applied force until maximum value (________ friction)

Answer 16

increases

limiting

Question 17

Friction is proportional to the ________ from the surface in contact

Answer 17

normal contact force

Question 18

Friction is zero when there is ________ applied even if one of the surfaces is rough

Answer 18

no force

Question 19

Friction is zero when surfaces are ________ even if a normal contact force is applied and/or object is moving

Answer 19

smooth

Question 20

Friction can be greatly reduced by the use of ________ on a surface

Answer 20

lubricants

Question 21

Define “tension”

Answer 21

A force which acts through a stretched rope/string/cable

Question 22

Define “normal contact force”

Answer 22

A force that is perpendicular to the surface of contact

Question 23

Define “upthrust”

Answer 23

An upward force exerted by a fluid (liquid/gas) on an object (fully or partially) immersed in the fluid

Question 24

Upthrust opposes ________

Answer 24

the object’s weight

Question 25

If an object floats, upthrust is ________ than weight

Answer 25

greater

Question 26

Define "density"

Answer 26

The mass per unit volume

Question 27

Formula to calculate density

Answer 27

m/v | [ mass / volume ]

Question 28

Formula to calculate average density (for a mixture of substances)

Answer 28

total mass / total volume

Question 29

What is the density of water

Answer 29

1.0g cm^-3 | = 1000kg m^-3

Question 30

An object stays at rest even when force is applied due to ________

Answer 30

static friction

Question 31

There is no resultant force → forces acting on an object are ________

Answer 31

balanced

Question 32

There is a resultant force → forces acting on an object are ________

Answer 32

unbalanced

Question 33

Define "resultant force"

Answer 33

The sum of forces acting on an object

Question 34

State Newton's First Law of Motion

Answer 34

An object at rest will remain at rest and an object in motion will continue in motion at constant speed in a straight line unless a resultant force acts on it

Question 35

Define "inertia"

Answer 35

A body's tendency to continue with its state of rest or motion

Question 36

The mass of a body is a measure of its ________

Answer 36

inertia

Question 37

The greater the mass of a body, the ________ its inertia

Answer 37

greater

Question 38

State Newton's Second Law of Motion

Answer 38

The resultant force acting upon an object is equal to the product of the mass and the acceleration of the object; the direction of the force is the same as that of the object's acceleration

Question 39

Formula to calculate resultant force

Answer 39

F = ma | [ resultant force = mass x acceleration ]

Question 40

When an object falls vertically through air, the upward resistive force R (air resistance or drag force) acting on it ________ as the velocity of the object increases

Answer 40

increases

Question 41

The object will fall with terminal velocity when...

Answer 41

the downward force of gravity (weight) on the object is equal to the upward resistive force R on the object

Question 42

Terminal velocity is the ________ velocity of the object

Answer 42

constant maximum

Question 43

State Newton's Third Law of Motion

Answer 43

The force which body A exerts on body B is always equal in magnitude and opposite in direction to the force which body B exerts on body A

Question 44

Forces always occur in pairs called ________ and ________ forces

Answer 44

action | reaction

Question 45

Each pair of action-reaction forces are always... (4)

Answer 45

- equal in magnitude - opposite in direction - acting on different bodies - of the same nature

Question 46

When force F is resolved into two components P and Q, P (the vertical force) = ________ Q (the horizontal force) = ________

Answer 46

F sin θ | F cos θ