Motion
Chapter 11
Motion

Motion is changing position against a
fixed point.


You can tell if something is moving if its
position changes against some background
that stays the same (frame of reference).
Displacement is the change in position of an
object.
Motion


Speed describes how fast an
object moves (scalar).
Velocity describes the speed
of an object plus the direction
in which it is moving
(vector).

Example: Tina the Llama
escaped at a speed of 4.5 m/s.
Tina the Llama escaped at a
velocity of 4.5 m/s to the north.
Motion
Calculating speed and velocity:
v=d/t
velocity or
speed
distance
time
Motion

The cheetah, the fastest of land animals, can run a
distance of 274 m in 8.65 s at its top speed. What is
the cheetah’s top speed?
v=
?
v=d/t
d=
274 m
v = 274 m / 8.65 s
t=
8.65 s
V = 31.7 m/s
Motion

Suppose the polar bear were running on land instead of
swimming. If the polar bear runs at a speed of about
29,880 m/h, how far will it travel in 10.0 hours?
v=
29,880 m/h
t*v=d/t*t
d=
?
d=v*t
t=
10 h
d = 29,880 m/h * 10 h
d = 298,800 m
Motion

The various types of tree sloths share the honor of being
the slowest-moving mammals. An average tree sloth
moves with a speed of 0.743 m/s. How long does it
take a sloth moving at this speed to travel 22.30 m?
v=
0.743 m/s
d=
22.30 m
t=
?
t*v=d/t*t
v*t=d
v
v
t=d/v
t = 22.30 m / 0.743 m/s
t = 30.0 s
Motion

The various types of tree sloths share the honor of being
the slowest-moving mammals. An average tree sloth
moves with a speed of 0.743 m/s. How long does it
take a sloth moving at this speed to travel 22.30 m?
v=
0.743 m/s
d=
22.30 m
t=
?
d
v * t
t=d/v
t = 22.30 m / 0.743 m/s
t = 30.0 s
Motion

Speed can be shown
on a distance-time
graph. The slope of
the line on this graph
will be equal to the
speed.
Acceleration

Acceleration is any change in velocity
(vector).
Acceleration
Calculating acceleration:
a = v / t
acceleration
change in
velocity
time
v = vf - vo
Acceleration

Acceleration can be
shown on a velocitytime graph.
The
slope of the line on
this graph will be
equal
to
the
acceleration.
Acceleration

A bicyclist accelerates at 0.89 m/s2 during a
5.0 s interval. What is the change in the
speed of the bicyclist and the bicycle?
a=
0.89 m/s2
Δv= ?
t=
Δv
5.0 s
a * t
Δv = a * t
Δv = 0.89 m/s2 * 5.0 s
Δv = 4.5 m/s
Acceleration

An automobile accelerates 1.77 m/s2 over 6.00 s to
reach freeway speed at the end of an entrance ramp. If
the car’s final speed is 24.44 m/s, what was its
initial speed when it began accelerating?
a=
1.77 m/s2
Δv= ?
t=
Δv
6s
a * t
Δv = a * t
Δv = 1.77 m/s2 * 6 s
Δv = 10.62 m/s
Δv = vf - vo
10.62 = 24.44 - vo
vo = 24.44 m/s – 10.62 m/s
vo = 13.8 m/s
Acceleration

The gravitational force between Mars and an object near its surface
is much lower than the force between an object on Earth’s surface
and Earth. If a dropped hammer’s speed increases from 0.0 m/s
to 15.0 m/s in 4.04 s, what is the acceleration due to the
gravitational force on the surface of Mars?
a=
a = v / t
?
Δv= vf – vo
= 15.0 m/s
– 0.0 m/s
= 15.0 m/s
t = 4.04 s
Δv
a * t
a = 15 m/s / 4.04 s
a = 3.713 m/s2
Forces

A force is a push or pull.

This push or pull causes an object to change its
velocity or acceleration.
Forces

The combination of all the
forces acting on an object is
the net force.



This combination will determine
whether the velocity of the
object will change.
An object accelerates in the
direction of the net force.
An object won’t accelerate if the
net force is zero.
Forces


Balanced Forces are equal in strength and cancel each
other out. Motion does not change. The net force is
zero.
Unbalanced Forces are not equal in strength and cause
an object to change its velocity or acceleration. The net
force is greater than zero.
Forces
Friction

Friction is an unbalanced force that opposes
motion. Friction resists the movement of one
surface past another.
Friction

There are three types of
frictions:



Sliding Friction: Occurs
when a solid surface slides
over another solid surface.
Rolling Friction: Occurs
when an object rolls across
a solid surface.
Static Friction: Occurs
between two objects that
touch but do not move.
Friction

Air Resistance is another type of friction. It
occurs between the surface of a moving object
and the air molecules.