Understanding Energy
Energy – the ability to create change
Outline
•	Quantities of motion
•	Velocity
•	Acceleration
•	Newton’s laws of motion
•	Inertia
•	F = ma
•	Action/Reaction
•	Work and Energy
Motion
•	What is motion?
•	Velocity = v = distance / time
•	Example: A car travels 200 miles in 3 hours.  What was its velocity?
•	V = 200 mi / 3 hr = 66.7 mph.
•	Convert to meters per second:
•	(66.7 mi / hr) x (1,600 m /mi) x ( 1hr / 3,600 sec.) = 29.6 m/s

Velocity Experiments
•	In class demo: Measuring the velocity of carts on a track.
•	At home experiment: Checking the speedometer on your car.
•	Measure the time T it takes to go from one mile marker to the next.
•	V = 1 mi / T (in minutes)
•	Example: T = .5 minutes
•	V = 1 mi / .5 min = 2 mi / min.
•	V = (2 mi /min) x ( 60 min /hr) = 120 mph!

Change in motion
•	Acceleration is the rate of change of velocity.
•	 a = change in v / time.
•	A car takes 10 seconds to go from 0 to 60 mph.  What is its acceleration?
•	 a = 60 mph / 10 sec = 6 mph/s
•	Convert units: (6 mi / hr) x (1600 m /mi) x (1 hr / 3600 s) = 2.67 m/s
•	 Then a = 2.67 m/s/s or 2.67 m/s2

Acceleration experiments
•	Accelerometer
•	Constant velocity means NO acceleration.
•	Acceleration is speeding up OR slowing down.
•	Acceleration is CHANGING DIRECTION, even if the speed is the same.
Acceleration due to Gravity
•	Aristotle – Heavier objects fall faster!
•	Galileo – If you account for air resistance and friction, all objects fall with the SAME acceleration!  
•	 a = g = 9.8 m/s2
•	Leaning tower of Pisa
•	Feather and ball in air, then in an evacuated tube
•	Feather and ball on the moon!
Newton’s three Laws of Motion
•	The law of inertia: The natural state for all objects is straight line uniform velocity.  A FORCE is required to change the velocity.
•	A FORCE produces a change in velocity proportional to the object’s MASS
•	F = m a
•	For every action, there is an equal and opposite reaction.
Understanding the 1st Law
•	How does an arrow fly?
•	Why do things naturally seem to slow down?  -- Force of Friction
•	Why do I need to keep my foot on the gas to keep going at a constant speed?  -- The Net Force (I.e. F1 + F2 = Net Force)
•	No acceleration = NO Net Force

•	….To be continued.