P5 Forces and Elasticity (page 205) Flashcards
What do stretching, compressing or bending do?
transfers energy
You can use forces to stretchthings too.
When you apply a force to an object you may cause it to?
stretch, compress or bend.
How do you get an object to stretch, compress or bend?
you need more than one force acting on the object (otherwise the object would simplymove in the direction of the appled force, instead of changing shape).
If an object has been elastically deformed, what do this mean?
it CAN go back to its original shape and length after the force has been removed.
What is the name called for objects that can be elastically deformed?
elastic objects (e.g. spring).
If an object has been inelastically deformed, what do this mean?
it doesn’t return to its original shape and length after the force has been removed.
Work is done when a force stretches or compresses an object, and what else?
and causes energy to be transferred to the elastic potential energy store of the object.
If it is elastically deformed, ALL this energy is transferred to the object’s elastic potential energy store see p.168.
If a spring is supported at the top then a weight is attached to the bottom, what happens?
it stretches.
The extension of a stretched spring (or other elastic object) means what?
it means it is directly proportional to the load or force applied - so F ∝ e.
This is the equation:
F = ke
Force (N)
k - spring constant (N/m)
e Extension (m)
see diagram of equation on page 205.
The spring constant depends on what?
the material that you are stretching - a stiffer spring has a greater spring constant.
The equation also works for compression (where e is just the difference between the natural and compressed lengths - the compression).
Extension is directly proportional to force, but this stops working when….
the force is great enough.
Is there a limit to the amount of force you can apply to an object for the extension to keep on increasing proportionally?
Yes
What do the graph show on page 205?
it shows force against extension for an elastic object.
On the Graph on page 205, there is a maximum force above which the graph curves, what do this show?
it shows it si no longer proportional to force. This is known as the limit of proportionality and is shown on the graph at the point marked P.
You might see graphs with these axes the other way around - extension-force graphs. The graph still starts has a straight part, but starts to curve upwards once you go past the limit of proportionality, instead of downwards.
A spring is fixed at one end and a force of 1 N is appled to the other end, casing it to stretch. The spring extends by 2cm. Calculate the spring constant of the spring (4 marks)
2 cm = 0.02 m (1 mark)
F = ke so k = F ÷ e (1 mark)
= 1 ÷ 0.02 (1 mark)
= 50 N/m (1 mark)
