Forces 3 - forces and elasticity Flashcards
Examples of elastic materials
Spring
Rubber band
Eraser
Playground surface
Tennis ball
Rubber gloves
Define elastic material
Elastic materials are materials that always return to their original shape, size and length after the stretching, bending or compressing force has been removed
How can objects change shape
They can change their shape by stretching, bending and compression
What is elastic deformation
Elastic deformation occurs when objects return to their original shape when the stretching, bending or compressing force is removed
Explain two properties of the spring that makes it suitable for use in the balance.
deforms elastically
(so) will return to its original
length / shape (after force is
removed)
compression is directly
proportional to the force
(applied)
(so) gives a linear scale
Materials that undergo elastic deformation/elastic materials
Springs
Define inelastic deformation
Inelastic deformation occurs when an object remains stretched and does not completely return to their original shape even when the stretching force is removed
In order to change an objects length or shape how many forces are needed to be applied
explain why
In order to change an object’s length or shape, then we have to apply more than one force
If we only applied one force to a stationary object, then the forces are no longer balanced
In this case the object would simply move (rather than changing length or shape)
what would happen if we only applied one force to a stationary object
If we only applied one force to a stationary object, then the forces are no longer balanced
In this case the object would simply move (rather than changing length or shape)
examples of inelastic materials/materials that undergo inelastic deformation
Plastic
State the equation that links force, extension and spring constant
F = k x e
Force -Newtons
Spring constant - k - N/m
Extension - e - metres
What happens when an elastic object is stretched or compressed
what is stored in the object?
When we stretch or compress an elastic object, we are using a force to do work.
In this case, elastic potential energy is stored in the object
work done = _____
only true _________________
work done = elastic potential energy store
only true when the object is not inelastic deformed
The variables of practical that investigates how the force applied to a spring affects the extension of the spring
Independent variable = Force applied to the spring
Dependent variable = Extension of the spring
Control variable = Spring (same spring used throughout the experiement)
Equipment for the experiment that investigates how the force applied to a spring affects the extension of the spring
Bosses
Clamps
Clamp stand
Heavy weight
spring
metre ruler
State the method for investigating how the force applied to a spring affects the extension of the spring
Set up the equipment using the G-clamp stand to secure the clamp stand to the desk
Place a heavy weight on the clamp stand to stop it from falling over
hang the spring from the clamp
use a second clamp and boss to fix a (half) metre rule alongside the spring
It is really important that the metre rule is vertical otherwise the reading will be inaccurate
The top of the spring must be at the zero point on the metre rule
The bottom of the spring has a wooden splint attached as a pointer. This pointer must be horizontal of the readings will be inaccurate
Now read the position of this pointer on the metre rule. This is the unstretched length of the spring
Hang a 1N weight on the spring.
Read the new position of the pointer on the metre rule.
Continue adding 1N weights to the spring and reading the position of the point
For each new force record the position of the
calculate the extension produced
To do this subtract the length of the unstretched spring from each reading
Unload the spring and repeat twice more to calculate a mean
State some risks assessment to this hookes law practical
Hazard: Clamp (stand, boss and masses) might fall off desk
Risk: injury to feet
Precaution: Use clamp to fix apparatus to the bench
Put (heavy) masses on the base/foot of the stand
Stand up so that you can move out of the way
Hazard: Spring could break / come loose
Risk: damage eye
Precaution: Wear safety goggles
Explain why it is important for the metre rule to be vertical
It is really important that the metre rule is vertical otherwise the reading will be inaccurate
How do we know that the extension is directly proportional to the force
The graph is a straight line passing through the origin (zero)
What type of relationship is there between force and extension
Extension is directly proportional to force
There is a linear (not a non-linear relationship) relationship between force and extension (this is because we get a straight line graph)
How do we know that the graph shows that the spring is elastic
This graph shows that the spring is elastic
This is because if we remove the weight, the extension returns to zero
When does the force/extension graph stop being a straight line
Why does the graph look like this
https://bam.files.bbci.co.uk/bam/live/content/zxbdng8/small
If we add too much weight to the spring
This shows we have reached the limit of proportionality
https://bam.files.bbci.co.uk/bam/live/content/zxbdng8/small
What type of graph is this
The graph is now non-linear
How can you know if you have overstretched a spring
If we took all the weight away, the spring would still show an extension
This is called inelastic deformation
By overstretching the spring we have reached _______
By overstretching the spring we have reached the limit of proportionality
How to calculate the spring constant using the graph
Gradient = change in y/change in x = ___/___ = ___ = e/f
Spring constant = f/e = 1/gradient = 1/__ = ___
The spring constant will be the same for any part of the graph as long as we do not exceed the limit of proportionality
How to calculate the work done in a spring
Ee = 1/2ke^2
What does the area under the force-extension graph equal
The energy in the elastic potential energy store of a stretched spring is equal to the area under a force-extension graph up to the point of the limit of proportionality
state Hooke’s law
The extension of an elastic object is directly proportional to the force applied, provided that the limit of
proportionality is not exceeded
How to calculate extension
Extension = final length - original length
Define limit of proportionality
The point beyond which the force applied to an elastic object is no longer directly proportional to the extension of the object
