# AS Physics - Mechanics definitions and experiments

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## Experiment 1 - Determining g

- Drop a mass from a range of different heights, using a metre ruler record these heights.

- Using a stopwatch determine the time taken for the masses to reach the ground

- s = 0.5 x a x t^2

a = 2s/ t^2

- Plot a graph of 2 x height (displacement) againts time squared

- Gradient of graph is g

- Errors are we are assuming air resistance is negligible and also the reaction time of the person timing can affect and invalidate our results.

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## Experiment 2 - finding centre of gravity of irregu

- Insert hole into object and hang freely from a clamp stand

- Add a small mass to a piece of string and hang this from the same point. This is a plumbline.

- Where plumbline comes to rest, draw a line along the string on the object.

- Repeat this from a different point on the object - suspend from different point and draw a line along the string where the plumbline comes to rest.

- Where the 2 lines intersect is the centre of gravity.

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## Experiment 3 - Determining Young's modulus of a ma

- Using a micrometer measure diameter of material you are extending and using pir^2 calculate cross sectional area of wire - repeat this every time a new load is added and wire is extended.

- Using a ruler measure the original length of the material you are extending.

- Hang a mass to the end of the material.

- Measure new length of the wire after each load (recording value of force) is applied and calculate extension = new - original length

now calculate stress = F/A and strain: x/L for your set of results

And use this information to plot a graph of stress against strain.

The gradient of the linear section of the graph is the Young modulus of the material

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## Experiment 4 - Determining Force constant of a spr

- Measure original length of spring

- Apply force to end of spring

- Record new length and calculate extension

New - orignal length.

F=kx    k = F/x

either use formula above or plot a graph or force against extension and the gradient of the linear section of this graph gives force constant.

Greater k - stiffer spring

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## Common Q #1

- Trilateration

-3 Satellites are used

- each satellite sends out a signal (em wave) which reaches a reciever in car and returns to the satellite.

- The time taken for the signal to return is determined.

- d = c x t is used to determine the distance of the car from each satellite

- where the 3 circles intersect is position of car

- The 3 circles represent the distance away from the satellite the car could be - but doesn't give us the direction so using 3 satellites allows us to determine position of car.

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## Common Q #2

Seatbelts - increase the time taken for the driver to stop moving, this reduces the acceleration of the driver and hence according to F=ma reduces the opposing force acting on the driver reducing the damage to the driver as a result. Also this prevents collisions with steering wheel etc.

Airbags - (exactly the same) - the rapid acceleration of the driver triggers airbags- they increase the time taken for the driver to stop moving, this reduces the acceleration of the driver and hence according to F=ma reduces the opposing force acting on the driver reducing the damage to the driver as a result. Also this prevents collisions with steering wheel etc.

Crumple zones - are designed to absorb  the impact of the collision and they use this force to elastically deform. They increase the time taken for the car to stop moving meaning that the acceleration of the car is reduced and hence the opposing force on the driver is also reduced. They also cause the force acting on the car to act over a greater distance which reduces the force acting on the driver and hence reduces damage to driver.

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## Common Q #2

Seatbelts - increase the time taken for the driver to stop moving, this reduces the acceleration of the driver and hence according to F=ma reduces the opposing force acting on the driver reducing the damage to the driver as a result. Also this prevents collisions with steering wheel etc.

Airbags - (exactly the same) - the rapid acceleration of the driver triggers airbags- they increase the time taken for the driver to stop moving, this reduces the acceleration of the driver and hence according to F=ma reduces the opposing force acting on the driver reducing the damage to the driver as a result. Also this prevents collisions with steering wheel etc.

Crumple zones - are designed to absorb  the impact of the collision and they use this force to elastically deform. They increase the time taken for the car to stop moving meaning that the acceleration of the car is reduced and hence the opposing force on the driver is also reduced. They also cause the force acting on the car to act over a greater distance which reduces the force acting on the driver and hence reduces damage to driver.

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## Common Q #3

A brittle material will behave elastically up until the breaking point- it shows no plastic region and obeys Hookes law till breaking point.

A polymeric material e.g. plastics do not obey Hookes law - they show no elastic region and she non-linear behaviour.

A ductile material - behaves elastically up until the elastic limit (obeying Hookes law) after this it will undergo plastic deformation and no longer obeys Hookes law.

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## Definitions

One newton - the force required to give a mass of 1kg an acceleration of 1metre per second every second.

One joule - the work done when a force of one newton moves its point of application 1m in the direction of the force.

One watt - the power when one joule of energy is tranferred every second.

Speed - distance per unit time

Displacement - distance in a particular direction

Velocity - Rate of change of displacement

Acceleration - rate of change of velocity

principle of moments - no resultant force, no resultant moment or torque

a couple - a pair of parallel, equal but opposite forces which tend to produce rotation only.

Torque - one of the forces x perpendicular distance between them

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## Definitions

Equillibrium - sum of clockwise moments = sum of anticockwise moments about the same point

moment - force x perpendicular distance from the line of action of the force to the pivot

Work done - force x distance moved in direction of force

power - rate of work done

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