Transcript Acceleration

Force and Motion
8th Grade
Investigations 5-8
Force and Motion
Unit 1: Acceleration
Velocity
• When physicists thing about how fast an
object moves, they study how far it moves
in a length of time (speed) and the
direction it travels.
• Velocity: the change of position per unit of
time.
Unit 1: Acceleration
Velocity Equation
v=
x
t
Unit 1: Acceleration
Displacement Review
•
t is displacement (xf - xi)
• Displacement can be positive or negative. Travel
toward a destination is positive displacement;
travel back toward the starting position is negative
displacement.
– The displacement at the end of a walk can be zero for
this reason.
Unit 1: Acceleration
Acceleration
• When we say something is changing
velocity we say it is accelerating.
• Acceleration: is a change of velocity per
unit of time.
– It is represented by a lowercase a.
Unit 1: Acceleration
Acceleration
• The unit of acceleration is change of
position per unit of time.
• Velocity is measured as meters per second.
v = m/s.
• Acceleration is measured as a = m/s/s.
Unit 1: Acceleration
Acceleration
• Acceleration can be positive or negative.
• Going faster: When an object is moving in
a positive direction, positive acceleration
results in increased velocity.
• Going Slower: When an object is moving
in a negative direction, negative
acceleration results in a reduction of speed.
Unit 1: Acceleration
Acceleration
• Acceleration is a change of velocity over
time.
QuickTime™ and a
dec ompres sor
are needed to s ee this pic ture.
Unit 1: Acceleration
Acceleration
• At what point during a roller coaster ride is
the coaster moving the fastest?
B
A
C
F
D
E
G
H
Unit 1: Acceleration
Acceleration
• Answer: The roller coaster is fastest at
position D. This is the bottom of the longest
descent, so the coaster has had the longest
time to accelerate.
(Refer to The Other Great Race)
Unit 1: Acceleration
Acceleration
• If you dropped a grape from a bridge, at
what point would it be traveling at its
greatest velocity? Why do you think so?
Unit 1: Acceleration
Acceleration
• Answer: The grape would be traveling the fastest
just as it hit the water (or ground) because objects
in free fall accelerate all the way down (or until
they reach terminal velocity.
• Terminal velocity is the point at which the force
of gravity is opposed by an equal force due to air
resistance.
(Refer to The Other Great Race)