P3.2 Using Physics To Make Things Work

Question 1

What is the relationship between forces and moments?

Answer 1

The larger the force the larger the moment.

Question 2

How do you obtain the maximum moment?

Answer 2

Push at 90 degrees to the lever

Question 3

When according to moments do objects not turn?

Answer 3

When the anticlockwise moment equals the clockwise moment.

Question 4

What are levers?

Answer 4

Force multipliers - less force needed to get the same moment.

Question 5

How do levers work according to moments?

Answer 5

They increase the distance from the pivot where the force is applied, meaning you need to apply less force for the same moment.

Question 6

What is the centre of mass?

Answer 6

Where the mass of an object is thought to be concentrated.

Question 7

What is a moment?

Answer 7

The turning effect of a force

Question 8

How do you find the centre of mass in a flat shape?

Answer 8

• Suspend the shape and a plumb line from the same point and wait until they stop moving.
• Draw a line along the plumb line
• Do the same thing but suspend them from a different pivot point.
• Where the two lines cross = centre of mass

Question 9

What happens to a freely suspended object?

Answer 9

It will swing until it returns to the point of equilibrium which is vertically below the point of suspension.

Question 10

What two properties make an object stable?

Answer 10

• Low centre of mass

- Wide base

Question 11

When does an object begin to tip over? (Think centre of mass)

Answer 11

When its centre of mass moves outside the tip of its base.

Question 12

Why does the centre of mass moving outside the tip of its base make an object tip over?

Answer 12

The line of the action of the weight of an object is outside its base which causes a resultant moment.

Question 13

What is the “time period” in pendulums?

Answer 13

The time taken for a pendulum to swing from one side to another and back again.

Question 14

What is the rule for the time period of a pendulum?

Answer 14

For a given pendulum, the time period for each swing is always the same.

Question 15

What is the relationship between the length of string of a pendulum and the time period?

Answer 15

The longer the string, the longer the time period.

Question 16

Give two uses of pendulums.

Answer 16

• Clocks

- Playground swings

Question 17

Where do you find the centre of mass in a symmetrical object?

Answer 17

Where the lines of symmetry cross.

Question 18

What property of a liquid makes it ideal for hydraulics?

Answer 18

They are virtually incompressible.

Question 19

What is the rule for pressure in liquids.

Answer 19

Pressure in a liquid is transferred equally in all directions.

Question 20

What is the rule for force in liquids?

Answer 20

A force applied in one point will soon be transmitted to other points.

Question 21

What do hydraulic systems do?

Answer 21

Act as force multipliers.

Question 22

Describe a hydraulic system.

Answer 22

• The system has two pistons, the first has a smaller cross sectional area.
• Pressure is exerted in the liquid in the 1st piston using a small force over a small area.
• The same pressure is transmitted to the 2nd piston which has a larger surface area so there will be a larger force (force = pressure x area)

Question 23

Where are hydraulic systems used?

Answer 23

• Car braking systems
• Hydraulic car jacks
• Manufactoring

Question 24

Where do objects travelling in a circle move?

Answer 24

They accelerate towards the centre of the circle.

Question 25

Why do objects travelling in a circle accelerate?

Answer 25

Their direction is constantly changing so their velocity (not speed) is constantly changing meaning they accelerate towards the centre of the circle.

Question 26

What is the centripetal force?

Answer 26

The resultant force that directs an object towards the centre of the circle.

Question 27

Name 3 forces that provide centripetal force.

Answer 27

• Gravitational force
• Friction
• Tension

Question 28

Give an example of centripetal force caused by friction.

Answer 28

A car going round the bend - friction between the tyres and the road causes a centripetal force.

Question 29

Give an example of centripetal force caused by tension.

Answer 29

A bucket on a rope - caused by tension in the rope.

Question 30

What factors affect centripetal force?

Answer 30

• Mass of the object
• Speed of the object
• Radius of the circle

Question 31

If mass —–, speed —— or radius —–, centripetal force will increase.

Answer 31

1) increases
2) increases
3) decreases