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Lecture 10

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

Department
Astronomy
Course Code
AS101
Professor
All
Lecture
10

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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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