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Motion Unit Class Notes
Motion – a change in position; an object is in motion when its distance from another
object (reference point) is changing
Speed – the rate at which an object is moving
Speed = Distance
Speed = Distance ÷ Time
Constant speed – same speed all the time
Average speed – speed for a complete trip
Instantaneous speed – speed at any one instant in time
Velocity – speed in a certain direction
Acceleration – rate at which velocity changes; either a change in speed or direction, or
Increase in speed
Decrease in speed (deceleration)
Change in direction
Acceleration = Final velocity – Start velocity (change in velocity)
(change in time)
Newton’s Laws of Motion
1. An object at rest will remain at rest, and an object in motion will remain in motion
unless acted upon by an outside force
Force – a transfer of energy; a push or pull that starts, stops or changes the
direction of an object
Friction – force that happens when the surfaces of matter move
past each other (Static, sliding, rolling, fluid)
- depends on the surfaces and the force pushing them together
Gravity – force that pulls objects towards each other
- depends on the mass of the objects and the distance between them
Inertia – an object’s tendency to keep doing what it is doing (rest or motion)
- resistance to change
- the greater the mass of an object, the greater its inertia
2. The net force on an object is equal to the product of its mass and its acceleration
Force = Mass x Acceleration
Newton = kg x m/sec2
3. When one object exerts a force on a second object, then the second object exerts a
force of equal strength on the first object.
- action/reaction law
- not like balanced net force on 1 object, these action/reaction forces act
on two different objects
Momentum – a measure of an object’s inertia of motion
Momentum = Mass x Velocity
Law of Conservation of Momentum – the total momentum of objects that interact
does not change, unless acted on by an outside force
Energy – the ability to do work or cause change
1. Kinetic energy (KE) – the energy of motion
- affected by mass and velocity
2. Potential energy (PE) – stored energy
- has the potential to do work or cause change
position - ex. Gravity or Elastic potential energy
sun’s energy – ex. food, wood, fossil fuels
Law of Conservation of Matter and Energy
- energy cannot be created or destroyed, it only changes form
- KE ↔ PE
Work – changing the energy of an object
Work = Force x Distance (moved in the direction of the force)
= Newton x meter
Power – rate at which work is done
Power = work ÷ time
Watt = Joules ÷ seconds
1 horsepower = 746 watts
Machine – a tool that makes work easier by……
1. changing the size of the force applied
- less force over a greater distance (ex. wheelbarrow)
- greater force over a smaller distance (ex. hammer)
2. changing the direction of the force applied (ex. pulley)
Work in = Work out
Mechanical Advantage (MA) – how many times the machine multiplies force
Types of machines
1. Lever – bar that pivots at a fixed point called a fulcrum
2. Wheel and axle –
3. Pulley – can be fixed or movable
4. Inclined plane
5. Wedge – an inclined plane that moves
6. Screw – an inclined plane wrapped around a cylinder to form a spiral