P2

AQA Physics Unit 2 Revision

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  • Created by: Uma
  • Created on: 20-12-10 19:36

Speed and Velocity 1

Speed (or velocity) = Distance / Time

Velocity is the same as speed, but in a given direction. To calculate velocity, use the above equation. Velocity is measured in metres per second (north, or appropriate direction). 

On a distance-time graph-

-When an object is stationary, the line is horizontal 

-When an object is moving at a constant speed, the line is a diagonal slope

-The steeper the line, the greater the speed of the object

-If something is returning back to its original place, the lines that represent it are ones that slope downwards

-A steepening curve represents speeding up

-A levelling off curve represents slowing down

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Speed and Velocity 2

Velocity-Time Graphs

The velocity of an object is its speed in a given direction. 


In a velocity-time graph-

-The gradient is the acceleration

-Steady speed is represented by a horizontal line

-The steeper the line, the greater the acceleration (or deceleration)

-The area under the graph is equal to the distance travelled in that time interval

-A curve means changing acceleration

-Speed is found by reading the value on the y-axis

 

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Acceleration

Acceleration = Change in Velocity / Time taken

Acceleration is how quickly the velocity of an object is changing. The unit of acceleration is m/s squared. And because this is an extra hard topic, here is an example:

A snail (haha, good one uma) accelerates steadily from 2 m/s to 6 m/s in 5.6 seconds. What is it's acceleration?

Acceleration = Change in velocity / time taken

                   = ( 6 - 2 ) / 5.6 = 4 / 5.6

                   = 0.71 m/s squared

 

                     d                                         change in v

                 s  x   t                                  a        x         t

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Newtons 1st Law of Motion

Balanced forces mean no change in velocity

Basically, as long as the forces of an object are balanced, it will just stay still, unless it is moving, in which case it will continue moving at the same velocity. 

 

When something is moving at a constant velocity, all the forces acting on it must be balanced.

 

To continue moving at a constant speed, there must be zero resultant force, not a constant overall force. 

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Newtons 2nd Law of Motion

A resultant force means acceleration

If there is an unbalanced force, the object will accelerate in that direction.

This acceleration can take five different forms; starting, stopping, speeding up, slowing down and changing direction. On a force diagram, the arrows will be unequal.

- the bigger the force, the greater the acceleration/deceleration

- the bigger the mass, the smaller the acceleration

- to get a big mass to accelerate as fast as a small mass, it needs a bigger force

Resultant Force = Mass x Acceleration

In most real situations, there are at least two forces acting on an object. The overall effect of these forces will decide the motion of the object. This overall force is called the resultant force. 

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Newtons 3rd Law of Motion

If object A exerts a force on object B, then object B will exert the exact opposite force on object A.

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Comments

Kathryn

Good notes is this AQA? It is useful anyway thanks x

Uma

Yeah its AQA, havent finished yet though, so keep checking!:)

Kathryn

okay thanks i will ..I am struggling with this unit at the moment so everthing helps ..i'm sitting my exam on january 19th ...have you sat yours yet?

Uma

Yeah i have mine on the 19th too, really scared! Nice picture by the way, Zainnn<3

Kathryn

good luck i am really nervous i don't want to resit :S ....i know right Niall <3

Uma

You will be just fine! Dont worry!!

Good luck:)

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