# Physics-end of year 9

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## Energy Transfers

Sound to Electrical-microphone

Electrical to Light-light bulb (heat is lost)

Chemical to Thermal-burning coal

Chemical to Kinetic-climbing a mountain

Kinetic to Sound-tuning fork

Elastic Potential to Kinetic-catapult

Chemical to Kinetic-fizzy drinks

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## Energy

• Chemcial energy
• Elastic potential energy
• Electrical energy
• Gravitational potential energy
• Kinetic energy
• Light energy
• Nuclear energy
• Sound energy
• Thermal energy
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## Waves

• The greater the amplitude, the louder the sound
• The greater the frequency, the higher the pitch
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## Pressure

• Stiletto heels are more likely to mark floors because they have a high pressure
• Camels have large, flat feet so they don't sink into the sand
• Tractors have large tyres and heavy lorries need eight rear wheels so they have a bigger area, a lower pressure and damage roads less

In water:

p=density(1000kg/m3  g=gravity  h=height

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## Wave uses and dangers

Microwaves-satellite TV, mobile phone signals.

Infrared-remote controls, infrared scanners and cameras. Causes burns

Visible light-LEDs, lasers. Danger to eyes

Ultraviolet-washing powders, produce vitsmin D-suntan. Bad for your eyes, can cause skin cancer

X-rays-check food for metal or stones, check bones and teeth. Radiation, can cause cancer, affect photographic film

Gamma rays-treat cancer. Remove elctrons from atoms so ions become unstable-causes cancer

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## Momentum

Momentum(kgm/s) = mass (kg) x velocity (m/s)

total momentum before collision = total momentum after collision

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## Work Done

• Work done (J)
• Force (N)
• DIstance (m)

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Speed-time graph

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## Hookes Law

The force of a steel spring is directly proportioanl to the force applied to it.

If the force is too large, the spring stretches beyond its limit of proportionality.

force applied (N) = spring constant (N/m) x extension (m)

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## Specific Heat Capacity

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## Gravity and weight

weight(N) = mass(kg) x gravity(N/kg)

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## Moments

The moment of a force is a measure of the turning effect of the force on an object

moment (Nm) = force (N) x perpendicular distance (m)

Example

A force of 50 N is exerted on a claw hammer of length 0.3m. Calculate the moment of the force.

Force = 50N x 0.3m = 15Nm

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## Forces

• If lift is bigger than gravity-plane will go up and forward
• If drag is bigger than thrust-plane will go forward but slow down
• If thrust is bigger than drag, and lift is bigger than gravity-plane will move forward and up
• If gravity is bigger than lift-plane will fall

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## Stopping Distance

Factors that affect sttopping distance:

• Tiredness, alcohol and drugs
• Speed of the vehicle
• Poorly maintained vehicles

Stopping distance = thinking distance (reaction time) + braking distance

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## Velocity and acceleration

change in velocity =the final velocity - the initial velocity

v=velocity u=initial velocity                                             velocity-initial distance  a=acceleration s=distance                 acceleration=   --------------------------------                                                                                                              2xdistance

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