Physics Forces

Question 1

List three things that forces do.

Answer 1

Forces explain why objects move, or why they don’t move at all.
Forces can also change the direction that objects are moving in and change their shape.

Question 2

Define gravity.

Answer 2

A non-contact force that acts between two masses.

Question 3

Define air resistance.

Answer 3

The force on an object moving through the air that causes it to slow down (also known as drag).

Question 4

Define a non-contact force.

Answer 4

Force that acts without direct contact (like magnetism).

Question 5

Define friction.

Answer 5

Force opposing motion which is caused by the interaction of surfaces moving over one another. It is called ‘drag’ if one is a fluid.

Question 6

Describe the difference between a contact force and a non-contact force.

Answer 6

A contact force acts when you are touching something ( like friction and air resistance). A non-contact force (gravity, magnetism) act without anything touching them.

Question 7

State the unit of force.

Answer 7

All forces are measured in newtons (N).

Question 8

How do you measure forces?

Answer 8

With a newtonmeter (sometimes called a spring balance).

Question 9

Forces always comes in pairs. The pairs are called….

Answer 9

interaction pairs.

Question 10

A force can be a …..or a …….

Answer 10

Push or pull.

Question 11

Upthrust is a contact force. Give an example.

Answer 11

The force of the water on you (upthrust) supports you when you float.

Question 12

Define resultant force.

Answer 12

Single force that can replace all the forces acting up an object and have the same effect.

Question 13

What are balanced forces?

Answer 13

When forces acting upon an object are the same size but act in opposite direction we say:

1) the resultant force is zero
2) the forces are balanced
3) the object is in equilibrium.

Question 14

State what equilibrium means.

Answer 14

The state of an object when all forces are balanced.

All stationary objects are in equilibrium.

Question 15

State the difference between balanced and unbalanced forces.

Answer 15

Balanced forces - forces acting in an object that are the same size but act in opposite directions.

Unbalanced forces - opposing forces on an object that are unequal.

Question 16

What are unbalanced forces?

Answer 16

When the forces acting on an object are not the same size, so they do not cancel each other out. Therefore, the resultant force is not zero.

Question 17

How do unbalanced forces change speed or direction? Give an example.

Answer 17

When accelerating, the driving force is bigger than the resistance force acting on the car, so the speed of the car increases.

When slowing down, the only forces acting on the care are resistive forces, such as friction and air resistance, so the speed of the car decreases.

Question 18

What is the definition of speed and how is it measured?

Answer 18

Speed is a measure of how far something travels in a particular time.

It can be measure in metres per second (m/s).

In cars, it can be measured in miles per hour (m.p.h.) or kilometres per hour (km/h).

Question 19

How do you calculate speed?

Answer 19

Speed (m/s) =
distance travelled (m) divided by the time taken (s).

Question 20

How can you work out the average speed?

Answer 20

By dividing the overall distance by the overall time that it took.

Question 21

What is meant by relative motion?

Answer 21

The speed of an object is always relative to the speed of the observer.

Question 22

How does a speed camera work?

Answer 22

It measures how long it takes a car to travel a certain distance by taking a photo at the start and end of the distance. Then it can calculate the car’s speed.

Question 23

Speed is relative. If two cars are travelling in the same direction, both at 30 mph, the speeds relative to one another is…..

Answer 23

zero.

Question 24

What does a distance-time graph show?

Answer 24

A useful way of showing how something moves - the distance something travels over a certain time.

Question 25

State what the slope of the distance-time graph shows you.

Answer 25

The slope of a distance-time graph tells you the speed. If the line is steep, the object is moving fast. If the line is not steep, the object is moving slowly.

Question 26

State what acceleration means.

Answer 26

Acceleration tells you how quickly your speed is changing.

Question 27

What factors affect the size of a gravitational force.

Answer 27

1) The mass of each object

2) How far apart they are.

If the mass is larger, the force is larger.

If the distance is larger, the force is smaller.

Question 28

Describe what is meant by a field.

Answer 28

A field is a special region where something, like a mass, experiences a non-contact force.

Question 29

What is the difference between weight and mass?

Answer 29

Weight is a force, so it is measured in newtons (N).

Mass is the amount of ‘stuff’ something is made up of. It is a measure of how hard it is to get something to move so is measure in kilograms (kg).

Question 30

How do you calculate weight using a formula?

Answer 30

Weight (N) =
Mass (kg) x gravitational field strength (g) (N/kg)

Question 31

State what is meant by gravitational field strength.

Answer 31

Gravitational field strength is about. 10 N/kg.
This is the force that acts on 1kg in the Earth’s gravitational field.

Question 32

Describe how the Earth stays in orbit around the Sun.

Answer 32

The force of gravity acting on the Moon keeps it in orbit around the Earth. It changes the direction of motion, not the speed.