Movement And Shape

Question 1

Elastic materials definition

Answer 1

Materials that return to their original shape

Question 2

Examples of elastic materials

Answer 2

Rubber

Lycra

Question 3

Plastic materials definition

Answer 3

Materials that do not return to their original shape when the force is removed

Question 4

Examples of plastic materials

Answer 4

Polymers
Play doh
Plasticine

Question 5

Brittle materials definition

Answer 5

Materials that will break rather than change shape

Question 6

Examples of brittle materials

Answer 6

Ceramics
Glass
Wrought iron

Question 7

What happens to the extension of a weight is added at the bottom of the spring?

Answer 7

Increases in length when it is stretched

Question 8

As we increase the amount of mass on the spring what happens?

Answer 8

The extension increases proportionally

Question 9

If the spring has not overstretched (for example one weight), what would the graph look like? The extension against the weight

Answer 9

It would be a straight line starting at the origin which has a constant gradient (which would mean the extension is directly proportional to the weight)

Question 10

Hooke’s Law

Answer 10

If a stretched object produces a graph with a constant gradient, we say that it obeys Hooke’s Law.

It is a law that says that the extension of an elastic object is directly proportional to the force applied.

Question 11

Do all springs behave the same?

Answer 11

No, some might extend more or less if the same force is applied.

For example, if Spring K extended more than Spring M, we would say that Spring M is the stiffest spring and spring K is the least stiff spring

Question 12

Stretching springs to their limits

Answer 12

If more weights are added, the springs might get ‘overloaded’ and the graph might look different.

It might stop becoming proportional and the line stops being a straight line. This point is called the Limit of Proportionality.

If it does stop being elastic, it happens at a point called the Elastic Limit. You can’t tell by looking at the graph but all we know is that it is beyond the limit of proportionality.

Question 13

Stretching Rubber

Answer 13

When stretched, rubber behaves differently to a metal spring. The line is a bit more irregular. It is stiff to begin with, then less stiff then gets stiffer again as more weight is added.

Question 14

Elastic potential energy

Answer 14

When a spring is stretched, we say that we ‘do work’ on it which means that we transfer energy to it. This energy is stored as Elastic Potential Energy in the stretched object.

Question 15

Load definition

Answer 15

The force applied

Measured in Newtons

Question 16

Extension definition

Answer 16

How much longer compared to original length - measured in mm, cm or m

Question 17

The centre of mass

Answer 17

An imaginary point where we can consider all of the mass of the object to be located. It is also the point where we can say that gravity acts on the object and is therefore also known as the Centre Of Gravity.

Question 18

What is a turning moment?

Answer 18

A turning effect of a force

Question 19

What does the turning moment depend on?

Answer 19

Size of the force

Perpendicular distance of the line of action from the pivot point of rotation

Question 20

How to see a moment in any situation

Answer 20

Look for the pivot point of rotation

Look for the force that will make it rotate

Question 21

Example of a spanner

Answer 21

The pivot point is where the screw is and the force is at the end of the spanner in which we hold to turn it. And therefore, the line of action is there at the end too.

The perpendicular distance is the distance from the line of action to the pivot

Question 22

Moments equation

Answer 22

Moment = Force x perpendicular distance from the line of action of the force to the pivot

Force is measured in Newtons
Distance is measured in metres

Triangle - moment at the top, force in the left and distance in the right

Question 23

Balancing moments

Answer 23

Moments make things turn so we describe the direction of turn as being anti-clockwise or clockwise.

When something is not rotating, the moments acting on the object would be balanced and we say that the object is therefore in equilibrium. And therefore, in order for it to be in equilibrium:

Sum of anti clockwise moments = sum of clockwise moments
This is known as the Principal of Moments

A seesaw is an example of this. If a person is sitting on the left and a person on the right. The person on the left is creating the anti-clockwise moment about the pivot and the right person is creating the clockwise moment about the pivot.

We can use this principal to work out stuff we don’t know. We just make it into an equation using anti clockwise = clockwise