SPEED/ACCELERATION

MOTION

WHAT IS MOTION?

HOW CAN YOU TELL IF AN OBJECT IS IN MOTION?

AN OBJECT IS IN MOTION WHEN ITS DISTANCE FROM ANOTHER OBJECT IS CHANGING.

A REFERENCE POINT IS AN OBJECT USED FOR COMPARISON,TO DETERMINE IF SOMETHING IS IN MOTION.

THE POSITION OF A PERSON OR OBJECT MUST BEDESCRIBED IN RELATION TO A STANDARDREFERENCE POINT.

EXAMPLE- A PERSON MIGHT BE IN FRONT OF OR BEHIND A DESK. THE DESK IS THE REFERENCEPOINT, AND IN FRONT OF AND BEHIND ARE THEREFERENCE DIRECTIONS.

Speed = distance/time

S = d/t

d

S t

S = d/t

t = d/s

d = s • t

EXAMPLE-

WHAT IS THE SPEED OF A CAR TRAVELING120 Km in 2 hours?

ANSWER-

if : s = d/t

s = 120 km / 2hrs.

s = 60 km/hr.

SPEED

THE SPEED OF AN OBJECT IS THE DISTANCE THE OBJECT TRAVELS IN A UNIT OF TIME.

SPEED = distance/time

s = d/t

CONSTANT SPEED- When the speed of an object does not change.

EXAMPLE- A train traveling down the track at a pre-set speed of 50 km/hr.

AVERAGE SPEED- When the speed of an object changes throughout a period of time. Speed

can vary.

AVERAGE SPEED = total distance traveled/total time elapsed

EXAMPLE- Lance Armstrong traveling through the mountains during the Tour du France.

Uphill he may be traveling one speed, downhill he may be traveling another. We can calculate his average speed throughout this portion of the race by

dividing his total distance by the total time.

VELOCITY

VELOCITY- must be described by specifying both the direction and the

speed of an object.EXAMPLE- A train was traveling 6

km/hr. in a NorthWest direction.

ACCELERATION

Acceleration- rate at which velocity changes.

- Increasing speed,

- Decreasing speed, or

- Changing direction

Slowing down can be referred to as:

- Acceleration,

- Negative acceleration, or

- Deacceleration

VELOCITY/ACCELERATION QUIZ

• What is the velocity of a car that traveled a total of 75 km North in 1.5 hours?

V = d/t therefore: 75 km/1.5 hr = 50 km/hr North

• A plane traveled 2.5 hours at a velocity of 1200 km/hr. in a SouthWest direction. What distance did it travel?

1200 km/hr • 2.5 hrs. = 3,000 km

• A girl is pedaling her bicycle at a velocity of 0.10 km/min South. How far will she travel in 2 hours?

0.10 km/min. • 60 min./hr = 6 km/hr 6 km/hr • 2 hrs. = 12 km

QUIZ continued . . .

• A car accelerates from a standstill to 60 km/hr in 10.0 seconds. What is its acceleration?

60 km/hr - 0 km/hr = 6 km/hr/s 10 s

• A car accelerates from 25 km/hr to 55 km/hr in 30 seconds. What is its acceleration?

55 km/hr - 25 km/hr = 1 km/hr/s 30 s

• A runner achieves a velocity of 12.1 m/s 9 seconds after he begins, what is his acceleration? What distance did he cover?

12.1 m/s - 0 m/s = 1.34 m/s/s 9 s

12.1 m/s • 9 s = 108.9 m

INSTANTANEOUS SPEED - Speed at any instant

- Constant Speed/Instantaneous Speed- does not change.

•Uniform motion - constant speed in a straight line.

•Accelerated motion – motion that is changing in speed or direction

•Circular motion - speed is constant but. the direction of motion is changing continuously.

TYPES OF MOTION

Motion GraphsMotion Graphs

Interpret The Graph Below:

Interpret The Graph Below:The graph shows an object which is not moving (at rest).

The distance stays the same as time goes by because it is not moving.

Interpret The Graph Below:

Interpret The Graph Below:The graph showsthat the objects distance increases as time passes.The object is moving and so it has velocity.

The straight line shows it is a constant (not changing).

Interpret The Graph Below:

Interpret The Graph Below:Just like the previous graph, this graph shows an object moving with constant velocity

Interpret The Graph Below:

Interpret The Graph Below:

The curve in the graph shows that the objects velocity is changing as time passes.

This is acceleration.

Interpret The Graph Below:

Interpret The Graph Below:In the first part of the graph the object is moving with constant velocity.

In the second part of the graph the object is at rest (not moving).

In the third part the object is again moving with constant velocity.

Interpret The Graph Below:

Interpret The Graph Below:

The graph showsthat the objects velocity does not change as time passes.

It shows constant velocity.

Interpret The Graph Below:

Interpret The Graph Below:The graph showsthat the objects velocity is increasing as time passes – it is accelerating.

The straight line shows that it is constant acceleration.

FINDING THE SLOPE OF A LINE

Click here for more review:http://www.usoe.k12.ut.us/curr/science/sciber00/8th/forces/sciber/intro.htm

How long does it take a marathoner to run 5 km, if he/she is keeping a pace of 0.150 km/min?

t = d/t

5 km/0.150 km/min

33.33 minutes

A bus travels 790 hm in 11 hours, what is the buses’ average speed?

S = d/t

790 hm/11 hours

71.82 hm/hr

Find the acceleration rate for a BMW that can accelerate from 35 m/hr to 120 m/hr in 0.04 hours.

A = final accel. - initial accel. time

120 m/hr. - 35 m/hr. 0.04 hours

A = 2,125 m/hr/hr

ADDITIONAL PROBLEMS

What is the distance a hiker walked if he hiked at a rate of 25 m/min. for 45 minutes?

Since: d = s • t

25 m/min. • 45 min.

1,125 meters