TOPIC 5 FORCES

Question 1

What is a scalar quantity?

Answer 1

● A quantity that only has a magnitude
● A quantity that isn’t direction
dependent

Question 2

What is a vector quantity?

Answer 2

A quantity that has both a magnitude and an associated direction.

Question 3

How can a vector quantity be drawn and what does it show?

Answer 3

● As an arrow
● The length of the arrow represents the
magnitude
● The arrow points in the associated
direction

Question 4

What is a force?

Answer 4

A push or pull acting on an object due to an interaction with another object.

Question 5

What are the two categories that all forces can be split into?

Answer 5

1. Contact forces (objects touching)
2. Non-contact forces (objects separated)

Question 6

Give three examples of contact forces.

Answer 6

1. Friction
2. Air resistance
3. Tension

Question 7

Give three examples of non-contact forces.

Answer 7

1. Gravitational forces
2. Electrostatic forces
3. Magnetic forces

Question 8

Is force a vector or a scalar quantity?

Answer 8

● Vector
● It has both a magnitude and an
associated direction

Question 9

Give three examples of vector quantities.

Answer 9

1. Velocity
2. Displacement
3. Force

Question 10

Give three examples of scalar quantities.

Answer 10

● Temperature
● Time
● Mass
● Speed
● Distance
● Energy

Question 11

What is weight?

Answer 11

The force that acts on an object due to gravity and the object’s mass.

Question 12

Formula and quantity of weight

Answer 12

Weight = mass x gravitational field strength
● The object’s mass
● The gravitational field strength at the
given position in the field

Question 13

What is the unit used for weight?

Answer 13

The Newton (N).

Question 14

What is the unit used for gravitational field strength?

Answer 14

N/kg

Question 15

What is meant by an object’s centre of mass?

Answer 15

The single point where an object’s weight can be considered to act through.

Question 16

What piece of equipment can be used to measure an object’s weight?

Answer 16

A calibrated spring-balance or newton- meter.

Question 17

What is the name given to the single force that is equivalent to all the other forces acting on a given object?

Answer 17

The resultant force.

Question 18

What does it mean if a force is said to do ‘work’?

Answer 18

The force causes an object to be displaced through a distance.

Question 19

What is the equation used to calculate work done? Give appropriate units.

Answer 19

Work done = Force x Distance
Work done (Joules), Force (Newtons), Distance (metres)

Question 20

What distance must be used when calculating work done?

Answer 20

It must be the distance that is moved along the line of action of the force.

Question 21

Under what circumstance is 1 joule of work done?

Answer 21

When a force of 1 Newton causes a displacement of 1 metre.

Question 22

How many Newton-metres are equal to 1 joule of energy?

Answer 22

1 Nm = 1 J

Question 23

SKIP

Answer 23

SKIP

Question 24

What occurs when work is done against frictional forces?

Answer 24

● A rise in temperature of the object occurs
● Kinetic energy is converted to heat

Question 25

Why does air resistance slow down a projectile?

Answer 25

● The object does work against the air resistance
● Kinetic energy is converted in to heat, slowing down the object

Question 26

Explain the relationship between the force applied and the extension of an elastic object.

Answer 26

The extension is directly proportional to the force applied, provided that the limit of proportionality is not exceeded.

Question 27

What is meant by an inelastic deformation?

Answer 27

● A deformation which results in the object being permanently stretched
● The object doesn’t return to its original shape when the force is removed

Question 28

State the equation relating force, spring constant and extension. Give appropriate units.

Answer 28

Force = Spring Constant x Extension
Force (N), Spring Constant (N/m) Extension (m)

Question 29

What type of energy is stored in a spring when it is stretched?

Answer 29

Elastic potential energy.

Question 30

What can extension be replaced with in the equation for spring force?

Answer 30

Compression

Question 31

What is an alternative name for the turning effect of a force?

Answer 31

A moment.

Question 32

State the equation used to calculate the moment of a force. Give appropriate units.

Answer 32

Moment of force = Force x Distance
Moment (Nm), Force (N), Distance (m)

Question 33

What distance measurement is used when calculating a moment?

Answer 33

The perpendicular distance from the pivot to the line of action of the force.

Question 34

If an object is in equilibrium, what can be said about the moments acting on the object?

Answer 34

The clockwise moments are equal to the anticlockwise moments.

Question 35

What three parts make up a lever system?

Answer 35

1. Load 2. Effort 3. Pivot

Question 36

How can a lever be used as a force multiplier?

Answer 36

If the distance between the effort and pivot is greater than the distance between the pivot and load, the force applied on the load is greater than the effort force. This is since the moment on both the effort and load must be the same.

Question 37

Give an example of when a lever may be used to multiply a force.

Answer 37

A wrench, which has a long handle so that the force applied by the user is multiplied.

Question 38

What determines the moment of a gear wheel?

Answer 38

The size of the wheel.

Question 39

Describe the moment and speed of a larger gear being driven by a smaller gear.

Answer 39

The larger wheel will rotate more slowly but will also produce a larger moment.