PHYSICSWHAT IS IT?

Measuring Motion•What is motion?•What is speed?• How or when is motion measured in life?

Motion is all around you!• How can you tell if something is in

motion?•You need a reference point• An object that appears to stay in one

place•When an object changes position over time relative to a reference point, that object is in motion!

What is SPEED?• Speed is the distance traveled by an object

divided by the time it took to travel that distance.

• SO… if the balloon traveled 50 meters in 10 seconds THEN…

50 meters meters10 seconds seconds

SI Unit for Speed

•meters/second = m/s• Kilometers/hour = Km/h• Feet/second = ft/s•Miles/hour = mi/h

• / = “per”

Average Speed

• Most objects do NOT travel at a constant speed SO we have a separate equation:

Average Speed = total distance total time

Recognizing Speed on a Graph

The actual distance traveled over time

The average distance traveled over time

360 Km 4h

90 Km/h¿

PRACTICE with word problems• An athlete swims a distance from one end of a 50 m

pool to the other end in a time of 25 s. What is the athlete’s average speed?

• STEP 1: Write the equation for average speed.

average speed = total distance total time

• STEP 2: Replace the total distance and total time with the values given, and solve.

average speed = = 2 m/s

50 m 25 s

MORE practice

1. Kira jogs to a store 72 meters away in a

time of 36 seconds. What is Kira’s average

speed?

2. If you travel 7.5 km and walk for 1.5 h,

what is your average speed?

3. An airplane traveling from San Francisco to

Chicago travels 1,260 km in 3.5 h. What is

the airplane’s average speed?

1.Kira jogs to a store 72 meters

away in a time of 36 seconds.

What is Kira’s average speed?

2. If you travel 7.5 km and walk for 1.5 h, what is your average speed?

3. An airplane traveling from San Francisco to Chicago travels 1,260 km in 3.5 h. What is the airplane’s average speed?

What is VELOCITY?• VELOCITY is the speed of an object in a particular

direction• SPEED VELOCITY• Velocity includes DIRECTION

SPEED VELOCITY 600 km/h 600 km/h West

Let’s think about it!

Imagine that two birds leave the same tree at the same time. They both fly at 10 km/h for 5 minutes, 12 km/h for 8 minutes, and 5 km/h for 10 minutes. Why DON’T the birds end up at the same place?

Changing Velocity

• An object’s velocity is constant (stays the same) only if its speed and direction do not change• SO… constant velocity is always motion along a straight line

• An object’s velocity changes if either its speed or direction changes• SO… changing velocity is always motion that is not along a straight line

Changing Velocity… of a bus

3 ways velocity can change1. A bus traveling 15 m/s south speeds up to 20

m/s south

2. A bus continues to travel at the same speed but changes direction to travel east

3. A bus slows down at the same time it swerves north to avoid a cat

Combining Velocities…same direction• When you combine two velocities that are in the

same direction, add them together to find the resultant velocity.

Person’s resultant velocity15 m/s east + 1 m/s east = 16 m/s east

Combining Velocities…opposite direction

• When you combine two velocities that are in opposite directions, subtract the smaller velocity from the larger velocity to find the resultant velocity. The resultant velocity is in the direction of the larger velocity.

Person’s resultant velocity15 m/s east – 1 m/s west = 14 m/s east