Physics: Structured Paper P2 - Topics 9 & 10

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Speed & Velocity

Speed is just how fast you're going.

Velocity however, must have the direction specified.

Velocity = Displacement / Time

s / v x t 

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Acceleration and Velocity Time Graphs

Acceleration is how quickly velocity is changing.

Acceleration = Change in velocity / Time taken

(v - u) / a x t

Time Graphs:

  • Gradient = Acceleration
  • Flat Section = Steady Speed
  • The area under any section is equal to the distance travelled in that time interval.
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Forces and Acceleration

A balanced force means steady speed and direction.

If the forces on an object are all BALANCED then it will keep moving at the SAME SPEED in the SAME DIRECTION
(if it starts of still, will stay still) 

A resultant force mean acceleration.

If there is an UNBALANCED force then the object will ACCELERATE in the direction of the force.

F = m x a

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Reaction Forces

If an object exerts a force on another object, that other object exerts the exact opposite force on the first object.

So, if you push a shopping trolly, it will push you back just as hard.
As soon as you stop pushing, so does the trolly. 

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Stopping Distances

Many factors effect your total stopping distance.

1) Thinking distance

- How fast you're going

- How you are feeling (tired, drunk, careless)

2) Braking distance

- How fast you're going

- How heavily loaded the veichle is

- How good your brakes are

- How good your grip is

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Car Safety

Momentum = Mass x Velocity

The greater the mass of an object, the greater its velocity.

Forces cause change in momentum..

Force acting (n) = Change in momentum (kgm/s) / Time Taken (s)

A large force means a faster change in momentum.

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Taking Risks

The risk of Simon falling in a ditch on the way home from Buffers night club is 1 in 500.

1 in 500 = 1/500

Fraction to decimal > 1 / 500 = 0.002

Decimal to percentage > 0.002 x 100 = 0.2%

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Work and Kinetic Energy

When a force moves an object, energy is transferred and work is done.

Work Done = Force x Distance

Kinetic Energy is energy of Movement

Kinetic Energy = 1/2 x mass x  velocity(sq)

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Electrical and Potential Energy

Electrical Power sources supply Electrical Energy.

Electrical Energy = Voltage x Current x Time

Potential Energy is Energy Due to Height.

Potential Energy = mass x g x height

Gravitational Potential Energy

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Conservation of Energy

There are two types of Energy Conservation.

"Energy Conservation" - using less fossil fuels because they might run out etc.

"Principle of Conservation of Energy" - major cornerstones of physics.

Energy can never be created or destroyed, only converted from one to another.
This is the only time energy is useful.

Eg. Light > Electricity (SOLAR PANEL)

When calculating the speed of a falling object we have to look at
Kinetic Energy gained = Potential Energy lost 

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Power is the "Rate of Doing Work" - ie. How much per second.


Power is measured in Watts.

Calculating your Power output.

Power = Energy Transferred / Time Taken

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Circular Motion

Circular Motion - Velocity is constantly changing.

The force towards the centre of the rotating object is CENTRIPETAL FORCE.

This force depends on Mass, Speed and Radius.

Centripetal Force = Mass x Speed / Radius

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Roller Coasters

Roller coasters transfer energy!

- At the top, the carriage has lots of gravitational potential energy.

- As the carriage goes down, this is converted to kinetic energy.

To go in a loop, the carriage needs CENTRIPETAL FORCE.

At the top of the loop, both weight and reaction force are acting in the same direction, so:

centripetal force = reaction + weight > REACTION = CENTRIPETAL - WEIGHT

At the bottom the loop, the two forces are acting in opposite directions, so:

centripetal force = reaction - weight > REACTION = CENTRIPETAL + WEIGHT

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Einsteins Relativity

Good example of theoretical ideas, not experimentation.


the speed of light, relative to you, is always the same, no matter how fast you're going in what direction.

time and space aren't fixed - they can both stretch or shrink.

A Good theory should make predictions that can be tested.


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