Chapter 3 : Forces and energy

Question 3

What are balanced forces?

Answer 3

It is forces that are equal and opposite in direction to eachother.

Question 4

If a ball is moving at a constant speed without accelaration, is it a balanced forces or unbalanced forces?

Answer 4

Balanced force.

Question 5

Link speed, distance and time as a formula.

Answer 5

Distance = speed x time

Question 6

What is the standard unit of time?

Answer 6

m/s

Question 7

Write the formula to calculate distance using speed and time.

Answer 7

Distance = speed x time

Question 8

Write the formula to calculate speed using distance and time.

Answer 8

Speed = distance / time

Question 9

Write the formula to calculate time using speed and distance.

Answer 9

Time = distance / speed

Question 10

What is a moment?

Answer 10

A moment is the turning effect of a force.

Question 11

Forces must always be __________

Answer 11

opposite

Question 12

Forces must always meet at _________

Answer 12

the pivot point

Question 13

State 2 factors that affect moments.

Answer 13

• Size of the force. The greater the force, the greater the moment.
• The distance from the position the force acts and the pivot.

Question 14

What is the formula for calculating moments?

Answer 14

Moments = force x distance

Question 15

What is the standard unit for moments?

Answer 15

Ncm

Question 16

Zara weighs 450N. Zara sits on one end of the seasaw at a distance of 1.5m from the pivot. Sofia weights 500N. She sits on the seesaw on the other side of the pivot from Zara. Calculate the distance from the pivot that Sofia must sit to balance the seesaw.

Answer 16

450N x 1.5m = 675Ncm
675Ncm / 500N = 1.35m

Question 17

Write the formula to calculate force using moment and distance from the pivot.

Answer 17

Force = moment / distance

Question 18

Write the formula to calculate the distance from the pivot using moment and force.

Answer 18

Distance = moment / force

Question 19

What is pressure?

Answer 19

Pressure is force per unit area.

Question 20

What is the standard unit for pressure?

Answer 20

N/m²

Question 21

State 2 factors affecting pressure.

Answer 21

• The force applied. The greater the force, the greater the pressure.
• The surface area. The smaller the surface area, the greater the pressure.

Question 22

Write an equation linking pressure, force and area.

Answer 22

Pressure = force / area

Question 23

A box has a weight of 60N. The area of the box in contact with the ground is 0.5m². Calculate the pressure that the box exerts on the ground. Show your working.

Answer 23

60N / 0.5m² = 120 N/m²

Question 24

A thumb tack has an area of 0.5mm² in contact with the wall. The pressure of 40 N/mm² is needed for the thumb tack to go into the wall. Calculate the force needed to push the thumb tack into the wall. Show your working.

Answer 24

0.5mm² x 40N/mm² = 20N

Question 25

Write the formula to calculate force using pressure and area.

Answer 25

Force = pressure x area

Question 26

Write the formula to calculate area using pressure and force.

Answer 26

Area = force / pressure

Question 27

Why does the pressure in a liquid change with depth?

Answer 27

It is because as you go depper in a liquid, there is more liquid above you. The weight of the liquid pushes on the particles of the lqiuid, causing the force on the particles to increase.

Question 28

What is altitude?

Answer 28

Altitude is the height above sea level.

Question 29

What is gas pressure?

Answer 29

Gas pressure is the force of the gas particles colliding with the walls of it's container.

Question 30

How does gas pressure increase?

Answer 30

The more particles there are in the gas, the more collisions happen within the container, causing the pressure to increase.

Question 31

State 2 factors that affect gas pressure.

Answer 31

- Temperature of the gas. - Volume of gas

Question 32

Define 'diffusion'.

Answer 32

The random movement of particles from a high concentration area to a low concentration area.

Question 33

Why does diffusion only occur in gases and liquids but not in solids?

Answer 33

It is because the particles in a solid are too tightly packed to move around whereas particles in liquids and gases are able to move around more freely.