Physics 30th January -7 th March

momentum kg m/s (p) = mass kg (m) x velocity m/s (v)

Conservation of momentum > a closed circuit system in which the total momentum before an event is the same as the total momentum after the vent

change of momentum = impact force x impact time

When vehicles collide force depnds on:

• mass
• change of velocity
• length of impact time

Longer impact time = reduced impact force

When 2 vehicles collide:

• they exert equal & opposite forces on eachother
• their total momentum ios unchanged

If the result is negative the force decelerates the object

To find irregular shapes centre:

• Using a pin pierce anywhere around the outside of the shape
• Put the pin in a cork and suspend it using a clamp
• Hang a weight on to the pin using a plumb line
• Draw a line where the string comes to rest
• Complete with at least one other point
• Draw a dot where the two lines cross > centre of mass

Centre of mass > the point at which the weight can be thought of as being cocncentrated

> A measure of the turning effect of a force

Moment (Nm) = force (N) x distance (m)

• Gears change the moment of a turning effect
• To increase the moment of a turning effect > small wheel needs to drive larger wheel
• Low gear = low speed

Why does a child sitting on a swing come to rest directly below the top of the swing?
If you suspend an object and then release it, it will come to rest with it's centre of mass directly below the poinbt of suspension.

• Hydraulics- the use of pressure in liquids
• Pressure (pascals) = force / area

• The bottom hole's water goes furthest as it has the most pressure on it (due to greter volume & hence weight) > open system

• Liquids are virtually incompresible
• Pressure in liquids are transmitted equally in all directions

The force in a hydraulic system depends on:

• The force exerted by the system
• The area of the cylinder which the force acts on
• The area of the cylinder that exerts the force

Pressure in liquid = height x density x gravity

Weight = upthrust

• If the upthrust is smaller > boat will sink

Upthrust depends on:

• amount of water displaced
• density of liquid

Amount of water displaced = volume of object

Crushing can demo:

• Air vapour gets cooled in water (takes up less room)
• leaves vaccum in can
• air pressure pushes in from outside casuing can to crush

pressure = hight x density x gravity

• Atmospheric pressure decreses with a higher altitude
• Less air above pushing down
• Less oxygen the higher you go as less particles

• Most        > magnetic
• Kids         > kinetic
• Hate        > heat
• Learning  > light
• G             > gravitational
• C             > chemical
• S             > sound
• E             > electrical
• Energy    > elastic
• Names    > nuclear

Energy transfer diagram: (TV)

Electricity > light + heat + sound

starting energy > energy used

useful energy > enrgy we want

wasteful energy > energy we don't use

Energy can only be transferred & transformed

work done = force x distance

weight = mass x gravity

Gravity > the force between 2 objects that have a mass

            > further away = further to fall = greater GPE

Gravitational potential energy = mass x gravity x height

(measured in joules)

Moving objects always have kinetic energy.

Affected by:

• velocity
• mass

Velocity > speed in a given direction

KE = 0.5 x mass x velocity^2

GPE lost = KE gained

Power > energy transferred in a certain amount of time

Watts > amount of joules transferred in 1 second

Energy = power / time 

How a lightbulb works:

• simple circuit with filament in middle
• electrons travel along circuit & continiously bump in to the tungstuns atoms which vibrate

Energy efficient light bulbs:

• electricity excites mix of gases inside bulb
• emites ultra violet light which is absorbed by fluorecent coating which transforms into light

No. of units (kWh) = power rating (Kw) x time appliance on (in hours)

• Always waste energy in energy change
• Wasted energy goes in to surroundings

The higher the initial hight the more enrgy is wasted through heat & soundmeaning there is less GPE.

more efficient = less wasted energy 

efficiency = useful output / total input > number between 0 & 1 (can be converted to percentage x100)

(dosen't have units > dividing joules by joules so cancel out)

Fuel > anything that can be burnt to produce light & heat

Chemical > (combustion) heat + light

Non-renewable:

• nuclear
• natural gas
• oil
• coal

Renewable:

• solar
• wave
• hydroelectric
• wind 

momentum (kg m/s) = mass x velocity

When a vehicle collides it depends on:

• mass
• change of velocity
• direction of impact

Longer impact = reduced force

When two vehicles collide:

• exert equal & opposite forces
• total momentum = unchanged

• All moving objets have momentum
• Measur of how hard something is to stop

Mass x 2 = speed / 2

• Scalar > size
• Vector > size & direction

Conservation of momentum = sum of momentum before a collsion or explosion is the same as the sum of monetum of tensions