# AS101 Lecture Notes - Lecture 10: Contact Force, Net Force, International System Of Units

by OC690588

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Motion:

oWhere is something and when is it there

oPosition is measured relative to a coordinate system

Speed:

oRate at which an object moves

oVelocity: Speed and direction

oUse SI units (m/s) unless otherwise asked

Acceleration:

oThe rate of change of velocity with time – change of velocity/time

oSince velocity has a direction, acceleration also has a direction

The acceleration of Gravity:

oAll falling objects have constant acceleration downwards (not

counting friction of air resistance)

oOn Earth acceleration of gravity, g=10 m/s2. Speed increases 10m/s

with each second of falling

Momentum:

oMass x velocity

oSince velocity has direction, momentum has direction

oNewton discovered a relationship between force and momentum

Force:

oA push or pull that acts on an object

oA force is exerted on an object (An object cannot push or pull on itself)

oA force on an object is exerted by an agent (The object can apply a

force back on the agent)

oA force can be either

A contact force (the agent touches the object)

A long range force (The agent does not actually touch the

object)

Newton’s three laws of motion:

oAn object remains at rest or at constant velocity unless a net force acts

to change its speed or direction

If an object is at rest or moving at constant velocity this does

NOT mean that there are no forces acting on it. It means that

the SUM of all the forces in all directions is 0.

oForce= rate of change of momentum with time

Force= mass x acceleration

oFor every force, there is always an equal and opposite reaction force

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