Physical Science: Ch 11 Notes
A. Speed and Velocity
Average speed – is the total distance traveled divided by the time it takes to
travel that distance.
Speed 
distance
time
During the time an object is moving, its speed may change, but this
equation tells you the average speed over the entire trip.
Instantaneous speed – the rate at which an object is moving at a given
moment in time.
This is difficult to measure without technology like a speedometer.
The metric unit for speed is “meters per second” or m/s.
The slope of a line on a distance-time graph is speed. A steeper slope
on a distance-time graph indicates a higher speed.
Physical Science: Ch 11 Notes
Practice Problems:
What was the speed of a turtle if it traveled 1 meter in 10 seconds?
What was the speed of a student who walked 40 meters in 24
seconds?
What was the speed of a student who took 10 seconds to move just
2 meters?
If a Corvette travels at a speed of 5 m/s, how many meters will it
travel in 135 seconds?
Velocity – the speed and direction in which an object is moving.
The metric unit for velocity is “meters per second” or m/s and it is
sometimes followed with a direction like “right” or “north”.
A change in velocity can be the result of a change in speed, a change in
direction, or both.
Physical Science: Ch 11 Notes
Practice Problems:
A deer is moving east to cross a highway. If the deer is moves 64
meters in 8 seconds, what is the velocity of the deer?
A mailman is driving up a hill. If his car travels 45 meters in 15
seconds, what is his velocity?
If Mrs. Casey runs east with a velocity of 7 m/s for 200 seconds,
how many meters will she travel (and in what direction)?
Physical Science: Ch 11 Notes
B. Acceleration – the rate at which velocity changes
-change in speed = acceleration
-change in direction = acceleration
-change in both speed and direction = acceleration
You calculate acceleration for straight-line motion by dividing the
change in velocity by the total time.
(final Velocity  initial Velocity)
Accelerati on 
Total Time
The metric unit for acceleration is “meters per second per second”
or “meters per second squared” (m/s/s or m/s2)
If the velocity increases, the acceleration is a positive value. If
the velocity decreases, the acceleration is a negative value
(called deceleration).
Physical Science: Ch 11 Notes
Practice Problems:
A sled begins at rest (0 m/s) at the top of a hill. If the sled
reaches the bottom of the hill 9 seconds later with a velocity of 7
m/s, what was the acceleration of the sled?
Mr. Swenson is in a hurry to get to home. If he is initially
traveling at 40 m/s but stomps on the gas and 6 seconds later is
traveling at 55 m/s. What was his acceleration?
Mark has to slow down a bit as he runs up a hill for cross
country. If he was initially running 7 m/s but slowed down to 5
m/s about 10 seconds later, what was his acceleration?
Physical Science: Ch 11 Notes
Constant acceleration – a steady change in velocity. This occurs when the
velocity of an object changes by the same amount each second.
Free fall – the constant acceleration of a falling object due to the Earth’s
gravity.
Objects falling near Earth’s surface accelerate downward at a constant
rate of 9.8 m/s2.
Each second an object is in free fall, its velocity increases by 9.8 m/s.
This increase in velocity is constant for all objects falling to earth, no
matter their mass, size, or shape (but air resistance makes it appear
that heavier objects fall faster).