Topic 8&9-forces Doing Work And Their Affect

Question 1

When is energy transferred and give an example?

Answer 1

Energy is transferred whenever things happen or when a force makes something move.

E.g electricity transfers energy to an electric light bulb, which then transfers every to surroundings by light and heat (thermal)

Question 2

What does work done mean?

Answer 2

A measure of energy transferred when a force acs through a distance.

Question 3

What does the amount of work done depend on?

Answer 3

The amount of energy transferred by a force is work done. The energy depends on the size of the force and how far the force has been moved.

Question 4

What is the equation to work out work done?

Answer 4

Work done = force x distance

Can be written as
E = F x d

Question 5

What are the units for the equation to work out word done?

Answer 5

Units for work done is: joules (J)
Force = Newtons (N)
Distance = (M)

Question 6

What does power mean?

Answer 6

Power is the rate at which energy is transferred. When energy is being transferred by forces, then Powers is also the rate of doing work.

Question 7

What is power measured in and what is it equivalent too?

Answer 7

Power is measured in watts.

1 watt = 1 joule of work done per second.

Question 8

How can power be calculated?

Answer 8

Power(W) = work done(J)/time taken(s)

P = E/t

Question 9

What is a contact force give an example?

Answer 9

Objects can interact with each other by exerting forces on each other. If the objects are touching, then the forces between the, are contact forces.

E.g When you stand on the floor, there is an upward force from the floor on you called the normal contact force.

Question 10

What is a non contact force and can you give an example?

Answer 10

Non contact force is when forces occur with out objects touching/interacting.

E.g a boat is floating on water the upthrust from the water is balanced by a non contact force called gravity. Gravity does not need to touch the boat to give it weight. The upthrust and the weight are both acting on the same object.

Question 11

Why does the moon stay in orbit around the earth?

Answer 11

Because the two bodies are attracting aching other. The force from the moon on the earth is the same as the force form the earth on the moon, but in the opposite direction. 🌍🌕 ➡️⬅️ ⬅️➡️

This is also an action reaction pair (Newton’s 3rd law)

Question 12

How can gravity be defined?

Answer 12

A force that occurs between any two objects that have a mass.

Question 13

How can the gravitational forces between two objects with mass be represented?

Answer 13

As vectors with arrows that show both the direction and magnitude.

Question 14

What is a force field? How does this link to the earth and moon?

Answer 14

The space around an object where it can affect other objects.

The moon and earth affect each other because the moon is within the earths gravitational field and vice versa.

Question 15

What non-direct forces affect objects?

Answer 15

Magnetism and static electricity(electric field)

Question 16

What effect does magnetism/magnets have in objects?

Answer 16

A magnet can attract objects made from magnetic materials including iron, nickel and cobalt. A magnet can attract or repel another magnet. The space around a magnet where it can affect other materials is called a magnetic field.

Question 17

What sort of field does static electricity have and how does this affect objects?

Answer 17

An object charged with static electricity has an eclectic field (electrostatic field) around it. The electric field can affect objects within it. Two objects with the same charge that are close to each other produce a pair of equal size forces acting in opposite directions.

Question 18

When are forces balanced?

Answer 18

If the forces are equal in size but in opposite directions, the resultant forces (or net force) is zero. The forces on the object are said to be balanced.

Question 19

What is a free body day diagram and what can it represent?

Answer 19

A diagram of of an object showing al, the forces acting upon it and the size and direction of forces.

A free body diagram for an aeroplane. The arrows represent force vectors. The direction of an arrow shows the direction of the force and the length of the arrow that represents its size. You can sketch this as a box.

Question 20

How can you use a scale diagram?

Answer 20

You can find the resultant force using a scale diagram.

Question 21

How do you draw a scale diagram to work out the resultant force?

Answer 21

• Draw arrows at the correct angles to represent the forces. The length of each arrow should represent the size of the force.
• Draw the lines to make a parallelogram
• The resultant force is the diagonal of the parallelogram. Measure the arrows to work out the size of the resultant force.

Question 22

What is a moment?

Answer 22

A turning force/rotating force is called a moment.

Question 23

What does the moment of a force depend on?

Answer 23

The size of the force and where the force is applied. The greater the force and the further it is applied from the pivot the greater the moment. The distance between the force and the pivot is measure at right angles to the direction of the force.

Question 24

What is the unit for a moment?

Answer 24

Newton metres (Nm)

Question 25

What is the equation for working out the moment of a force?

Answer 25

Moment = force x distance

Question 26

State what equilibrium means?

Answer 26

When a situation is not changing because all the things affecting it balance out.

Question 27

What does the the sum of clockwise moments equal?

Answer 27

Sum of clockwise moments = sum of anti clockwise moments

Question 28

What is a lever?

Answer 28

A bar that pivots about a point and is used to transfer a force.

Question 29

Explain how the rotational effect of a force can also be transmitted?

Answer 29

It can be transmitted by gears. A gear is a system of toothed wheels. The teeth interlock so that turning one turns the one in contact with it. If gears of different sized are used the speed of rotation or the force transmitted can be changed.

Question 30

John walks directly up a hill and he takes 12 minutes to get to the top. Hazel walks up the hill on a shallower hill that zig zags as it goes up. She takes 15 minutes to get to the top.

Explain who has exerted the greater power, and who has transferred more energy while getting to the top of the hill. Include any assumptions in your answer.

Answer 30

Power is the rate at which you’re doing work, and is measured in Watts. In climbing the hill they are doing work against gravity, and the energy transferred is the force (their weight) multiplied by the distance moved in the direction of the force (up the hill). If they both have the same weight, as they have both climbed the same distance, in theory they have transferred the same amount of energy. John exerted the greater power though because he gained the height in a shorter time.

However, this is answer may not be correct is their weights are different. It also assumes that the human body is totally efficient, which it is not. As Hazel was walking for longer, she will waste more energy and so will have transferred more energy altogether.