Forces And Elasticity (HOOKE’S LAW)

Question 1

When you apply force to an object, three things may happen. List them.

Answer 1

Either they’ll stretch, compress or bend

Question 2

What’s the requirement for an object to deform?

Answer 2

There must be more than one force acting upon it

Question 3

What will happen instead of changing the shape if only one force acts upon the object?

Answer 3

It’ll just move in the direction the force pushes or pulls it in, instead of changing the shape.

Question 4

Explain what it would mean if an object were to be elastically deformed

Answer 4

If an object could return to its original form (shape and length) after the force is removed, then that object was elastically deformed.

Question 5

Explain what an elastic object is. List an example.

Answer 5

An elastic object is an object that’s been elastically deformed. An example would be a spring.

Question 6

What does it mean for an object to be inelastically deformed?

Answer 6

This is when an object cannot return to its original shape and form after the forces are taken away.

Question 7

How is work done with elastic and inelastic objects?

Answer 7

Work is done when a force stretches/compresses an object and causes energy to be transferred to the objects elastic potential energy store. If the object is elastically deformed, then ALL the energy would transfer to its elastic potential energy store.

Question 8

What is the relation between extension and force?

Answer 8

They’re in direct proportion.

Question 9

What is the equation used to prove that force is in direct proportion to extension?

Answer 9

F = ke or kx

Question 10

What does the F stand for in F = ke or kx? Give units.

Answer 10

F stands for force. Units: newtons

Question 11

What does the k stand for in F = ke or kx? Give units.

Answer 11

k stands for spring constant. Units are N/m

Question 12

What does the e or x stand for in F = ke or kx? Give units.

Answer 12

e/x stands for extension, units: metres

Question 13

The spring constant can change depending on a certain thing. What is that thing? Explain with an example.

Answer 13

Spring constant will depend on the material you’re stretching. A stiffer material/object, would give a greater spring constant (more force, less extension)

Question 14

What does e/x mean in F = ke or kx? (hint: I’m asking for what it means not what it stands for)

Answer 14

Extension is the difference between the objects natural length and the length after it deforms. It only applies to stretching and compressing.

Question 15

How would F = ke or kx work for compression?

Answer 15

e/x would have to be the difference between natural length and compressed length.

Question 16

In what scenario would F = ke or kx not apply?

Answer 16

If the force is great enough, it won’t apply anymore

Question 17

True or False: there isn’t a maximum amount of force you can apply for the extension to keep increasing proportionately.

Answer 17

False

Question 18

There is a graph showing force against ext. for an elastic object. Where can you find the limit of proportionality?

Answer 18

The point where the straight, diagonal line meets a curve

Question 19

What happens if you go above the maximum for the applied force?

Answer 19

Above the maximum and the extension and force will no longer be directly proportional.

Question 20

What is the limit of proportionality on a graph?

Answer 20

It’s a point what marks the maximum for applied force. Above that point, the graph curves and ext. and force are no longer proportional.

Question 21

Normally, graphs for force against ext. will show force on the y axis and ext. on the x axis. What would happen if it were swapped?

Answer 21

The line would still go in a straight, diagonal line up until the limit of proportionality but instead of curving downwards it’d curve upwards as force will be greater than ext. past that point.

Question 22

What is Hooke’s law?

Answer 22

Hooke’s law states that force and extension are directly proportional to each other unless force exceeds the limit of proportionality.

Question 23

What happens if the limit of proportionality is exceeded?

Answer 23

The object (if elastic) will be deformed and will not go back to its original shape. In fact it is now inelastic.

Question 24

What is the formula for Hooke’s law?

Answer 24

F = ke or F = kx

Question 25

What is spring constant? Where do you find it on the graph

Answer 25

It’s the gradient of a the force vs extension graph. The stiffer a spring, the steeper the gradient. Spring constant is a measure of how stiff a spring is

Question 26

What is spring constant? Where do you find it on the graph

Answer 26

It’s the gradient of a the force vs extension graph. The stiffer a spring, the steeper the gradient. Spring constant is a measure of how stiff a spring is

Question 27

Define Hooke’s law

Answer 27

Extension is directly proportional to force exerted, provided the elastic limit/limit of proportionality isn’t reached

Question 28

Explain how the limit of proportionality affects a spring stretching

Answer 28

A single spring should return to its original length after being stretched. Force = extension is in motion and this all happens because the spring is elastic. However, after a certain force is exerted on it, it’ll start to extend more than the force acting on it. This is where the elastic limit is reached. If limit of proportionality is reached, the spring is then deformed and it now possesses the inability to return to its original shape. The spring is now ineleastic

Question 29

Which store is energy of a stretched spring stored in? What’s the unit?

Answer 29

Elastic potential energy (unit Joules)

Question 30

List three ways that you can calculate energy stored in a stretched spring and list the conditions for all three ways

Answer 30

Way one: you have to have a graph. If you have one, the area underneath the line/graph is the energy. This is normally in a shape of a triangle if the line obeys Hooke’s law.
Way two: use formula Ep = 1/2F *e. You can only use this formula if extension is in METRES
Way three: use formula Ep = 1/2k *e squared. To use this, e HAS TO BE IN METRES. And everything to do with E in the equation. So k also has to be in N/m.