P2.3 Flashcards
What is an elastic body
Objects that return to their original shape when the deforming force is removed.
What is a plastic body
Objects that do not return to their original shape when the deforming force is removed.
What is Hooke’s law
The extension of a body is directly proportional to the force applied, as long as the limit of proportionality is not exceeded.
Hookes law (formula)
F = k x e
Force applied = spring constant X extension
Spring constant - unit N/m
How to find spring constant from a force - extension graph
The gradient
Where is the limit of proportionality found on a force - extension graph
JUST BEFORE the line starts to curve
What is the elastic limit
is the point after which, the body is permanently
deformed when the deforming force is removed.
Where is the elastic limit found on a force - extension graph
comes slightly after the limit of proportionality.
Does a stiff spring have a large or small spring constant
A large spring constant
= The greater the spring constant, the more force required to extend it per metre, thus the stiffer the spring.
Greater the gradient of a force - extension graph
Greater spring constant
Stiffer material
Describe the behaviour of an elastic band and copper wire, as they are stretched.
Explain your answer using their force-extension graphs.
ELASTIC BAND
- When the elastic is first stretched, it is quite stiff.
Applying further force causes the elastic to become less stiff.
Finally it becomes stiff again with further force and extension.This is illustrated by the gradient of the F-e graph initially being steep, becoming less steep and then becoming steep again.
What is elastic potential energy
energy stored by an elastic body, that has been stretched
How does the spring constant effect the EPE of a body
The bigger the spring constant , the stiffer the material, the more force it needs to bring about the same extension… more EPE it has.
EPE equation
EPE = ½ x k x e2
Weight equation
Weight = mass x gravitational field strength
Units of gravitational field strength
N/kg
What is gravitational potential energy
the energy stored by a body, whenever it is raised through a height in a planet’s gravitational field.
EXTRA -
This is because in order to lift a body, a force must be applied up to counter its weight.
Thus work is done on the body (energy is transferred to it), where the final energy is in the form of GPE.
GPE equation
GPE = m x g x h
What is moment (definition)
Moment of a force is a measure of its turning effect.
Moment of a force (formula)
Moment = Force x PERPENDICULAR distance
Units of moment
Nm
How to increase a moment of a force
- Increasing the size of the force
2. Increasing the perpendicular distance from the pivot
When is a body in equilibrium
No resultant force or resultant moment acting upon it
What is the principle of moments
The sum of clockwise moments about any point = the sum of anti clockwise moments
What is a lever + how do they work
A FORCE MULTIPLER
- A small effort (applied force) on one side of the lever,leads to a large load (force exerted) on a body on the opposite side of the pivot.
Mechanical advantage formula
Describe and explain how moving the load nearer to the pivot changes the mechanical advantage or a lever
Moving the load closer to the pivot will decrease the perpendicular distance and thus decrease the moment of the load about the pivot. So we need to apply that moment from the left side.
Thus, a smaller effort can be applied to lift the same load as the distance is larger on the left side.
Hence, the mechanical advantage increases.
What are gears + how do they work
MOMENT MULTIPLIERS
Force applied between gears is the same,but as ⊥ distance changes, moment of force changes.
What happens when you transition from a small gear to a larger gear
Small Gear to Big Gear…… moment increases… larger acceleration(car starting from rest, cycling uphill)
What happens when you go from large gear to small gear
Big Gear to Small Gear…… moment decreases… smaller acceleration(car travelling at high speed, cycling on level ground)
Suggest and explain which cog on the front wheel you should use to go uphill
You use the smallest cog (12 cm) (1 mark)
because you need a large mechanical advantage. (1 mark)
The force you exert moves the small cog by a larger distance but produces a bigger force that moves a smaller distance. (1 mark)
Why do hydraulic machines work
Hydraulics machines only work becauseliquids are incompressible.
As a liquid is incompressible forces are transmitted through them, without loss, in all directions.
What does a hydraulic machine do
Hydraulics machines use the pressure exerted in liquids to multiply forces and apply them at a distance.
How does a hydraulic machine work
Two pistons are connected by a pipe full of fluid.
A force is applied to piston 1, acts over area 1,and creates a pressure within the fluid.
The same pressure acts at piston 2, over an area 2.
Area 2 > Area 1… output force increased.
Area 2 < Area 2… output force decreased.
