Chapter 3Chapter 3

Linear MotionLinear Motion

Description of MotionDescription of Motion

instantaneous speed - the speed that something has at any one instance

interval timecovered distance total = speed average

timedistance Speed

The average speed for a trip might be 53 miles/hour.

...or 70 miles/hour on the open road.

However, during this trip your instantaneous speed might have been 0 miles/hour at a stoplight...

Example Question

1. What is the average speed of a cheetah that sprints 100 meters in 4 seconds?

2. How about if it sprints 50 m in 2 s?

What are the units of speed?

miles/hour…………….mph

kilometer/hour……….km/h

meters/second……….m/s

furlongs/fortnight?

Example Question

If a car moves with an average speed of 60km/h for an hour, it will travel a distance of 60 km.– (a) How far would if travel if it moved

at this rate for 4 hours?– (b) For 10 h?– (c) Would if be possible for the car to

have an average speed of 60km/h and never exceed a reading of 60km/h?

Velocity = {speed with a direction}

Examples:

70 mph is a speed.

70 mph North is a velocity.

VelocityVelocity

Acceleration - rate of change in velocity due to change in speed or direction

AccelerationAcceleration

interval time velocityof change =on Accelerati

Example:• 9.8 meters/second2 downward

Example Question

"She moves at a constant speed in a constant direction.”

Say the same sentence in fewer words.

Answer: “She moves at constant

velocity.”

The speedometer of a car moving to the east reads 100km/h.

It passes another car that moves to the west at 100km/h.

Do both cars have the same speed?

Do they have the same velocity?

During a certain time, the speedometer of car reads a constant 60km/h.

Does this indicate a constant speed?

Constant velocity?

Example Multiple-Choice Questions

1. The two measurements necessary for calculating average speed are

(a) acceleration and time.(b) velocity and time.(c) distance and time.(d) distance and acceleration.

2. What is the average speed of a horse that gallops a distance of 10 kilometers in a time of 30 minutes?

(a) 10km/h(b) 20km/h(c) 30km/h(d) more than 30km/h

3. What is the acceleration of a car that maintains a constant velocity of 100km/h for 10 seconds?

(a) 0 km/h s(b) 10 km/h s(c) 10 m/s2

(d) 1000 km/h s

Free fall is a state of falling free from air resistance and other forces except gravity.

Free FallFree Fall

(a) you drop an object from rest at t=0.

(b) velocity acquired = acceleration time

v = g t

(c)

For Free Fall...For Free Fall...

timetimeonAccelerati21 = traveledDistance

2gt

21d

6. Dan drops a stone down a well and sees it hit the water 4 seconds later. Neglecting air resistance, how deep is this well? (a) 9.8 m (b) 19.6 m (c) 78.4 m (d) 156.8 m (e) 39.2 m

7. Dan drops a stone down a well and sees it hit the water 4 seconds later. Neglecting air resistance, what is the speed of impact of the stone?

(a) 9.8 m/s (b) 19.6 m/s (c) 4.9 m/s

(d) 78.4 m/s (e) 39.2 m/s

End of Chapter 2

timedistance Speed

Velocity = {speed with a direction}

interval time velocityof change =on Accelerati

g = 9.8 m/s2 downward

v = g t

Free FallFree Fall

2gt

21d