# Mechanics

- Created by: PinkPanzer
- Created on: 05-12-11 12:12

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**Key words**

- String- Inextensible and has no mass
- Particle- Has no size but does have mass
- Rigid Body- Has size but does not change shape
- Smooth- Has no friction
- Rough- Has friction
- Light- Has no mass
- Inelastic/Inextensible- Does not stretch

**Kinemetics in one dimension**

- In a Displacement-time graph, the velocity is calculated by working out the gradient (y/x =velocity)
- Velocity-time graphs have a gradient equivalent to acceleration. (y/x=accelration)
- Area under a Velocity-time graph= Distance travelled
**v=u+at****s=((u+v)t)/2****v^2=u^2+2as****s=ut+0.5at^2**or**s=vt-0.5at^2**- Where s=displacement, u=initial velocity, v=final velocity, a=acceleration, t=time.
- Formulae only work when acceleration is constant
- Acceleration due to gravity(g)= 9.8 metres per second

**Kinematics in two dimensions**

- Positions, velocities and accelerations can be expressed in the form x
**i**+y**j** - Constant acceleration equations (shown above) can be used in two dimensions. Once in the
**i**direction and once in the**j**direction. Adding both**i**and**j**together gives a vector. - Magnitude and Direction of vectors can be calculated using trigonometry and pythagoras.

**Forces**

- Force is a vector quantity
- Resultant force=two or more forces added together using its perpendicular components.
- Particle is in
**equilibrium if resultant=0** - Weight= mass x acceleration due to gravity
**(W=mg)** - Frictional force between two surfaces in contact will act in a opposite direction to the…

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