S-9

Define the term motion. Give an example of something in

motion. How do we know an object is in

motion? How do we know if we are in motion

even if our eyes are closed?

Chapter 2Motion

SPS8 Students will determine relationships among force, mass, and motion.a. Calculate velocity and acceleration.

11.1 Distance and Displacement

What is needed to describe motion completely?How are distance and displacement different?How do you add displacements?

11.1 Distance and DisplacementI can determine an appropriate frame of reference and decide if an object is moving

How do we know an object is moving?

Frame of reference Motion is always relative (compared to) something That something is called the Frame of Reference for us usually the earth)

11.1 Distance and DisplacementI can determine an appropriate frame of reference and decide if an object is moving

How do we know an object is moving? Frame of reference

We choose a frame that makes sense. Using the ground as a frame, the ball is moving forward Using the truck as a frame of reference, the ball goes up then back down

11.1 Distance and DisplacementI can explain the difference between distance and displacement

Distance – the length of a path between two points

Displacement – straight line distance (and direction) between the start and end

Example: Travel 3.5 miles south

PHET Vector

Addition

11.1 Distance and DisplacementI can add one dimensional vectors for displacement, velocity, and acceleration

Adding Displacements (vector addition)

Vector – has number value and direction

If the vectors aren’t in a straight line, then we have to use trigonometry to add the vectors

11.2 Speed and Velocity

How are instantaneous speed and average speed different?How can you find the speed from a distance-time graph?How are speed and velocity different?How do velocities add?

SR-71 BlackbirdSpeed: 2070 mphor 920 m/s

11.2 Speed and VelocityI can calculate the average speed for a moving object.

Speed – ratio of distance to time Measured in meters per second (m/s) Average Speed

Example: A car travels 25 km in 0.2 hours, then 45 km in 0.3 hours. What is the average speed?

Total distance and then total distance

TimeTotal

ceDisTotaledAverageSpe

.

tan.t

dv

tv

4525

t

kmv

70

3.02.0

70

kmv

hr

kmv

5.0

70 hr

kmv 140

11.2 Speed and VelocityI can calculate the average speed for a moving object.

Practice: A person jog 400 meters in 192 seconds, then 200 meters in 132 seconds, and finally 100 meters in 96 seconds. What is the joggers speed?

t

dv

96132192

100200400

vs

mv

420

700 s

mv 67.1

11.2 Speed and VelocityI can calculate the average speed for a moving object.

Practice: A train travels 190 kilometers in 3.0 hours, and then 120 kilometers in 2.0 hours. What is its average speed?

t

dv

0.20.3

120190

vhr

kmv

0.5

310 hr

kmv 62

11.2 Speed and VelocityI can calculate the average speed for a moving object.

A speedometer does not measure average speed, it measures instantaneous speed.

11.2 Speed and VelocityI can calculate speed from a distance time graph.

A distance time graph can be used to determine speed.

The slope of the graph (distance divided by time) is average speed

GizmoDistance vs. Time

11.2 Speed and VelocityI can list two ways velocity changes and show these changes by graphs or diagrams.

Velocity – speed in a direction (vector)

Velocity changes with either A change in speed A change in direction

Velocity is added by vector addition (like displacement)

11.3 Acceleration

How are changes in velocity described?How can you calculate acceleration?How does a speed-time graph indicate acceleration?What is instantaneous acceleration?

11.3 AccelerationI can define acceleration.

Acceleration is a change in velocity, so Change in speed▪ Either getting faster▪ Or getting slower

Change in direction▪ Turning

Measured in meters per second squared (m/s2)

11.3 AccelerationI can calculate the acceleration for an object changing speed.

Calculating Acceleration – divide the change in velocity (speed) by the total time

Example: A ball rolls down a ramp, starting from rest. 4 seconds later, it’s velocity is 13 m/s. What is the acceleration of the ball?

First, what is the initial velocity? 0 m/s

timetotal

velocityinchangenAccleratio

.

..

t

va

t

vva if

s

a4

013

sa s

m

4

13 225.3

sma

11.3 AccelerationI can calculate the acceleration for an object changing speed.

Practice Problem 1

A car traveling at 10 m/s slows down to 3 m/s in 20 seconds. What is the acceleration?

t

vva if

sa

20

103

sa s

m

20

7 235.0

sma

11.3 AccelerationI can calculate the acceleration for an object changing speed.

Practice Problem 2

An airplane travels down a runway for 4.0 seconds with an

acceleration of 9.0 m/s2. What is its change in velocity during this time?

t

va

s

vsm

0.40.9 2

vs

sm 0.40.9 2

smv 36

11.3 AccelerationI can determine acceleration from a speed-time graph.

Reading a Speed-Time graph The slope of the graph (rise over run)

is the acceleration Straight upward – positive constant

acceleration Straight downward – negative constant

acceleration (slowing down) Flat – constant speed, no acceleration Curved – changing acceleration

11.4 Free Fall

How does gravity cause acceleration?

Free Fall – when an object is falling under only the influence of gravity

The acceleration due to gravity on the surface of the earth is 9.80 m/s2

So our acceleration equation becomes

Everything else is the same

11.4 Free FallI can calculate using the acceleration due to gravity.

t

vv if

sm

280.9

Problem 1 How fast will a rock dropped from the top of the empire state building be going after 8.0 seconds?

11.4 Free FallI can calculate using the acceleration due to gravity.

t

vv if

sm

280.9

s

v fsm

0.8

080.9 2

s

v fsm

0.880.9 2 fsm vs 0.880.9 2 fs

m v4.78