# FORCES AND MOTION NOTES

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Speed and velocity

Equation:

Distance     (m) / (km)

Speed =

Time (s)/(h)

DON'T BE FOOLED BY 1 HOUR AND 30 MINUTES,

E.g. Ursain Bolt ran 100 metres in 9.58 seconds.

What was his speed?

= 100/9.58 = 10.4384 m/s

E.g. How quickly would it take him to complete if he ran 100m  at a speed of 11.2 m/s

= 100/11.2 = 8.9286 s

Exam hints

• Units for speed NEED to be m/s or km/s

Distance time graphs

The gradient of the graph can be used to calculate the speed at different points

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Speed  describes how fast an object travels

(the time taken for an object to cover a certain distance)

Velocity

Velocity is speed in a given direction

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EXAM TIPS!

•
• Check the labels --> velocity/speed
• The area under the line tells the distance travelled

Acceleration

The change in velocity over time

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*If it is a negative number then it is decelarating.*

Forces

Newton's law of motion

1. Inertia- things like doing what they are already doing
1. If the forces on an object are equal, it is either stationary  or moving at a constant speed.

Forces are measured in Newtons (N)

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Usually the bigger the arrow the bigger the force  but obviously on the diagram above it is not drawn to scale

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• Forces can change the direction of things

Force = mass x acceleration

(N)    =  kg     x   m/s2

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Also if the examiner asks to write the equation DON’T  write the triangle out.

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This is an obvious one but…

Gravity is the force of attraction objects have for each other because of their MASS

The bigger the mass, the bigger attraction

No resultant force equals to terminal velocity

When an object falls the two forces that affect it are:

1. Gravity
1. Air resistance

So this is the step by step guide that you have to learn:

At first the gravity force is greater than the air resistance force so the object accelerates in…