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P4 ­ Explaining Motion
Speed, Distance, Velocity and Acceleration
Speed is the distance travelled in a certain time.
To find the speed of an object you need to know the distance it travels (meters) and the time it takes
(seconds). Use the formula:
This formula triangle shows that to find the...
Distance Time Graphs
Important notes:
Gradient = Speed
Flat sections are where it is stationary
The steeper the gradient, the faster it's going
Downhill sections mean it's coming back toward the starting point
Curves represent acceleration or deceleration
A steeping curve means it's speeding up
A levelling-off curve means it's slowing down
Displacement-time graphs are almost the same ­ except the
Gradient tells you the velocity.
The displacement of something is its distance in a given direction, from its starting point, at
any particular moment in time.
Displacement can be positive or negative. This means that an object can be going in one
direction or an opposite direction.

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Velocity is a useful measure of motion, as it describes both the speed and direction.
Instantaneous velocity is its speed and direction at a given moment in time.…read more

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The Three Types of Friction:
1. Friction between solid surfaces which are gripping
This is the friction that lets you walk around ­ the friction between your shoes and the ground allows
you to push against it and move forward. If there was no friction then you would slip and slide
2. Friction between solid surfaces which are sliding past each other
You can reduce sliding friction and gripping friction by putting a lubricant like oil or grease between
the surfaces.
3.…read more

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So if the arrows come in opposite pairs, and they are all the same size, then the forces are
balanced…read more

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Resultant Force
In many situations, the force acting on an object are not all the same ­ meaning that they are
The resultant force is the overall force acting on an object ­ the force you get when you take into
account all the individual forces and their directions. It's this force that decides the motion of the
object ­ whether it will accelerate, decelerate or stay at a steady speed.…read more

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When a resultant force acts on an object, it causes a change in momentum in the direction of the
force. The change of momentum it causes is proportional to the size of the force and the time it acts
for. So, the bigger the force and the longer it acts for, the bigger the change in momentum.
When a force moves an object it does work and energy is transferred to the object.…read more

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Increase in Kinetic energy = Work done
So if work is done on an object, then energy is transferred to that object which will make it start
moving or to move faster. In physics, energy is always conserved. This means that you can't create or
destroy energy ­ it just gets transformed from one kind of energy to another.…read more



Really helpful, thanks!

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