Forces - elasticity, pressure, moments Flashcards
Hookes law equation
force = spring constant x extension
what is deformation
a change in shape
what is elastic deformation
where the deformation is reversed when the force is removed
what is inelastic deformation
where the deformation is not fully reversed when the force is removed - there is a permanent change in shape
examples of elastic and inelastic deformation
elastic - rubber band
inelastic - metal can being squashed
in order to change the length or shape of an object, what has to be done
more than one force has to be applied on it
what would happen if we only applied one force on a stationary object
the forces would no longer be balanced, so the object would just move rather than change shape
what is stored in elastic objects
elastic potential energy
describe how to investigate the relationship between the force and extension for a spring (equipment)
- a clamp stand
- 2 clamp bosses
- two clamps
- heavy weight
- metre rule
- spring
- pointer (wooden splint)
why should the pointer be horizontal
because if its not, readings would be inncaurate
describe how to investigate the relationship between the force and extension for a spring practical
- Set up a clamp stand with 2 clamp bosses and 2 clamps
- Place a heavy weight on the clamp stand
- Attach a metre rule and a spring to the stand
- Allign the top of the spring to zero on the metre rule
- Read the position of the pointer (wooden splint on the bottom of the spring) on the metre rule
- this is the unstretched length of the spring - hang a 1N weight on the spring
- read the position of the pointer on the metre rule
- Keep adding 1 N weights every time and reading the pointer position
- To work out the extension produced, subtract the length of the unstretched spring from each reading
- Plot the extension against the weight
- identify the the range of force over which the extension of the spring is directly proportional to the weight hanging from it
why do we place a heavy weight on the stand
to stop it from falling over
control variables of elasticity practical
- placement of ruler
- placement of spring
what should the results be from the elasticity experiment
extension is directly proportional to the weight
- straight line going through the origin
- linear relationship- straight line
what happens if you add too much weight to the springs
even after the weights are removed, the spring will still have some extension, so it’ll be inelastically deformed
how can you find the spring constant using a graph
dividing the force (weight) by the extension
when will the spring constant not be the same on a point on graph
if we exceed the limit of proportionality
when does extension happen
when an object increases in length
what are compressions
regions of high pressure due to particles being close together, happens when an object decreases in length
what is spring constant a measure of
the stiffness of a spring up to its limit of proportionality or elastic limit
what is limit of proportionality
the point beyond which Hooke’s law is no longer true when stretching a material
what is an elastic limit
the furthest point it can be stretched or deformed while being able to return to its previous shape.
what does a higher spring constant result in
a stiffer spring
what causes an object to rotate
a force or a system of forces
what is a moment
the turning effect of a force
how to calculate the moment of a force (newton metres)
moment = force x distance
what is the rule for distance when calculating a moment
the distance has to be perpendicular from the lines of action of the force to the pivot
what do we know about the moment of an object if it is balanced
the anticlockwise and clockwise moment are equal
the force x distance in the clockwise direction = the force x distance in the anticlockwise direction
how can we explain (using moments) why an object can topple
- if you tilt an object, there comes a point where the line of action of the weight lies just outside the base of the object
- now, there’ll be a resultant (unbalanced) moment acting on the block
- this’ll cause the block to topple
what are levers
force multipliers that allow us to lift heavy objects by applying a relatively small amount of force
what do gears and levers do
transmit the turning effect of a force
what does the turning effect in gears depend on
the distance between the edge of the gear and the centre
how often does the smaller gear turn compared to the bigger one
2:1
what are elastic materials
materials which will always return to their original length or shape if we take away the forces acting on them
force equation using spring constant
F =ke
what type of energy is stored in an elastic material
elastic potential energy
elastic potential energy is equal tooo….
work done
why should the metre rule be vertical
so we get accurate readings
what is the unit for moment
Nm
examples of things you find gears in
cars
