# 8 Motion and Force

This is a unit which really many find quite difficult. To help yourself out you must learn Newton’s 1st, 2nd and 3rd law of forces. Without this knowledge you cannot succeed in explaining or reasoning out most questions. Also there is a basic principle of coplanar forces producing a resultant and therefore acceleration. It is simple as it is…

Big – Small = Resultant in the Direction of Big!

There is an easy way to remember the laws….

1)     Inertia – “Objects” – don’t want to move but when moving find it difficult to stop

2)   F=ma – or ratio F/m = a which is more appropriate. The acceleration on a fat person is found as the ratio of the force of the push to the mass of the person

3)   Opposites – for every force their is an opposite. Fat person on chair pushing down, chair pushes up to support weight with equal and opposite force.

#### Resources

8.1 Force and acceleration

8_1_Newtons Laws (Help sheet)

8.2 Using F=ma  (or F/m = a)

8.3 Terminal speed

83_Terminal Speed Practical (Worksheet – Advanced Extension)

8_3_Termnial V Results for BB (Excel Results)

https://www.hypertextbook.com/facts/JianHuang.shtml

https://www.passmytheory.co.uk/learningcentre/stoppingdistance.aspx

8.5 Vehicle safety

85_Extension_Vehicle_safety (HSW Worksheet)

85_Practical_Sports Shoe (HSW Worksheet)

## AS_9_2_Pully Explaination.flv

Simple idea of F=ma shows that Big-Small = acceleration in direction of Big.

So F = ma ............... T - mg = ma etc....