Forces

Question 1

Define a scalar quantity and give 2 examples

Answer 1

It is a quantity which only has size or magnitude

eg a kg of apples or temperature of 30 degrees

Question 2

Define a vector quantity

What type of quantities are vectors?

Answer 2

It is a quantity which has size or magnitude and direction

Forces are vector quantities because you can push with a force of 240N to the left or to the right

Question 3

What is meant by the term velocity

Answer 3

It is a speed in a certain direction

Question 4

What is the difference between speed and velocity

Answer 4

Speed is a scalar quantity and velocity is a vector.
if we say an aeroplane is travelling at 180m/s then we are describing it’s speed. If we say it’s travelling at 180m/s due east then we are describing it’s velocity.

Question 5

What is the difference between distance and displacement?

Answer 5

Distance is a scalar quantity and displacement is a vector.
For example the distance from Thornbury Castle to Warwick castle is 71 miles. If we add a direction of NE then it becomes a displacement.

Question 6

How is a vector drawn?

Answer 6

vectors are represented by arrows. The size of the arrow represents the magnitude of the vector and the direction is shown by the direction of the arrow.
For example if an object has 2 forces acting on it and one is bigger than the other the arrows will be different lengths. The arrows will show the direction of the force.

Question 7

What is a force?

Answer 7

A force is a push or a pull. therefor it is a vector quantitty because it has magnitude and direction.

Question 8

What are the three things that force can change? - give examples to illustrate your answers.

Answer 8

1. Shape eg stretching a spring
2. Speed eg throwing a ball increases it’s speed
3. Direction eg batting a ball can change it’s direction

Question 9

What is a contact force?

Answer 9

A contact force is one which can be exerted between two objects when they touch
eg your hand on a ball

Question 10

What are the four main contact forces?

Answer 10

1. Normal contact force, the force which supports an object resting on a surface eg your phone on a table.
2. Friction, the force which opposes objects moving relative to each other eg the tyres on your bike and the road surface
3. Tension the force exerted through a rope when we pull on it eg when towing a car
4. Air resistance also called drag. It is the force acting on an object moving through the air. eg a car driving- you can feel it if you hold you hand out of the window.

Question 11

What is a non contact force?

Answer 11

They are forces which act between objects which are physically separated.

Question 12

Identify and describe 3 non contact forces.

Answer 12

1. 1. Gravitational. Gravity is the force which pull objects down towards the earth.
2. Electrostatic. These forces act between charged objects eg when you rub a balloon and can stick it to a wall.
3. Magnetic. Magnets attract objects made of iron or steel towards them.

Question 13

What units are used to measure forces?

Answer 13

They are measured in newtons (N)

kilonewtons (kN) and meganewtons (MN) are used to measure large forces

Question 14

Describe the term weight, how is it calculated?

Answer 14

Weight describes the pull of gravity on an object
It is calculated as W = mg
Weight = mass x gravitational field strength.

Question 15

What is gravitational field strength?

Answer 15

The earth produces a gravitational field which pulls objects towards it. Near the surface this is 9.8 N/kg

Question 16

What is the relationship between weight and mass

Answer 16

They are directly proportional, so if your mass decreases so does your weight.
Your weight changes if the gravitational field changes - so in space where there is a very low gravitational field your weight is less but your mass remains the same.
weight ∝ mass

Question 17

What is the name of the point on an object through which the weight is considered to act.

Answer 17

The centre of mass

Question 18

What is meant by the term resultant force

Answer 18

It is the single force which is a combination of all of the other forces acting on an object. It has the same effect as all of the forces acting together.
eg two people pushing an object, one pushes with a force of 300N the other 400N the resultant force is 700N
OR two teams pulling against each other on a tug of war rope, one pulls with a force of 2500N the other 2700N the resultant force is 200N

Question 19

What is a free body diagram?

Answer 19

A diagram which shows the magnitude and direction of all of the forces acting upon an object. The forces act through a point, the centre of mass.

Question 20

Resolving forces

Answer 20

If you are given a diagram with a vector and an angle.

1) Measure the length of the vector and calculate the scale used. Divide the number of cm by the number of Newtons to get a ratio
2) Complete the right angled triangle and measure the lengths of the horizontal and vertical sides.
3) From the scale calculate the forces. Multiply the length in cm by the ratio to get the answer in Newtons

Question 21

How could you define the term work?

Answer 21

It is when a force acts on an object and causes it to move through a distance.
W = F x s
Work (J) = Force (N) x distance moved in the direction of the force (m)

Question 22

Give some examples of how energy can be transferred during work

Answer 22

1. Dragging a box along the floor is work and because you are working against the frictional forces of the ground the temperature of the floor and the box both rise.
2. If you lift up an object and put it on a shelf you are doing work. The energy expended by your muscles is transferred to the object as gravitational potential energy.

Question 23

What happens when you apply a single force to an object.

Answer 23

It could change it’s speed or direction.

Question 24

How many forces do you need in order to change the shape of an object?

Answer 24

At least 2 forces are need to change the shape of the object. If those forces are balanced then the object will remain stationary.

Question 25

If an object like a spring has been stretched and returns to its original length what is it called.

Answer 25

Elastic deformation.

Question 26

What is inelastic deformation?

Answer 26

If an object like a spring has been stretched and does not return to its original length

Question 27

What is the name given to the difference between the stretched and unstretched lengths of a spring

Answer 27

Extension

Question 28

What is the equation used for elastic deformation

Answer 28

Force(N) = spring constant (N/m) x extension (m)
F = k e

Question 29

Explain the term spring constant

Answer 29

Spring constant tells us how stiff and difficult to stretch or compress a spring is. It is measured in N/m. So if a spring has a spring constant of 180N/m then it will take a force of 180 newtons to stretch or compress the spring 1 m

Question 30

What is the equation used to calculate the work done when compressing or stretching a spring?

Answer 30

elastic potential energy(N) = 1/2 x spring constant(N/m) x extension² (m)
Ee = 1/2k e²

Question 31

What is the definition of the term limit of proportionality

Answer 31

It is the point beyond which a spring will be permanently deformed.
Elastic deformation stops and inelastic deformation begins.

Question 32

What type of energy does a stretched spring store?

Answer 32

Elastic potential energy

Question 33

Explain how energy is converted when a drinks can is squashed.

Answer 33

If it is slightly squashed and only elastic deformation has occurred then elastic potential energy is stored in the can which is then used to pop the can back into shape. However once it has reached the limit of proportionality and the can is permanently deformed there is no elastic potential energy stored in the can. Work has been done as the atoms have been moved past each other to create a new shape. This work causes a small rise in temperature in the can.

Question 34

What is elastic potential energy?

Answer 34

It is the type of energy stored in a stretched spring before it reaches its limit of proportionality.