PhysicsPhysics

Motion, Speed, and Velocity

SC Standards Covered

S8P2. Students will be familiar with the forms and transformations of energy.

c. Compare and contrast the different forms of energy (heat, light, electricity, mechanical motion, sound) and their characteristics.

S8P3. Students will investigate relationship between force, mass, and the motion of objects.

a. Determine the relationship between velocity and acceleration.

Motion

• When an object changes its position, motion has occurred.– Distance- How far an object has moved.– Displacement-How far an object has moved in

relation to its starting point.• Consider direction

Example: One runner travels along a straight line for 500 meters. At the end of the run her distance and displacement is 500 m. While a runner who runs on a circular path for 500 meters can have a distance of 500 meters but a displacement of 0 meters.

Speed- Distance an object travels per unit of time

Relationships between speed, distance, and time:

Speed = Distance/ Time = d/ t » Constant Speed- speed does not change

over time» Average Speed- speed of motion when

speed is changing

Avg Speed = Total Distance/ Total Time

» Instantaneous Speed- speed at any given moment in time (speedometer)

Physics Circle

DistanceVelocity

SpeedRate Time

Km mi m ft

hr min secKm/hr mi/hrm/s ft/min

Graphing Motion

• Graph distance on the y-axis and time on the x-axis

Slope = Slope = riserise = = distancedistance = speed = speed

run timerun time

Distance - Time Graph

• If something is not moving, a horizontal line is drawn.

• If something starts out slow and then speeds up, its change in speed can look like this.

Learning Checkpoint

This graph shows several stages of motion:

•Stage 1: 100 m in 10 s

•Stage 2: 50 m in 10 s

•Stage 3: 150 m in 20 s

Calculate the speed as indicated by each of the colors.

Calculate the average speed.

What is the total distance?

Solution

Stage 1: S= d/ t

100 m/ 10 s= 10 m/s

Stage 2: S= d/t

50 m/ 10 s= 5 m/s

Stage 3: S= d/t

150 m/ 20 s= 7.5 m/s

Ave Speed= Tot d/ Tot t

300 m/ 40 s= 7.5 m/s

Distance = 300 meters

Velocity

• The speed and direction of an object’s motion.

Ex: 88 km / hr southwest

Practice

1. It takes Sally 2 hours to drive the 170 km to the mall. What is her average speed?

2. Bob needs 30 minutes to get to work. If he works 40 km from home, what is his average speed in km/hr? (hint: extra thinking is required)

3. Sue drives 70 mph on the Interstate. How long will it take her to get to Orlando if it is 350 miles away?

4. If Jaquan has to be in Alabama by 6pm and it is noon, how fast would he have to drive to make the 800 km trip in time?

Practice

1. It takes Sally 2 hours to drive the 170 km to the mall. What is her average speed?

Practice

2. Bob needs 30 minutes to get to work. If he works 40 km from home, what is his average speed in km/hr? (hint: extra thinking is required)

Practice

3. Sue drives 70 mph on the Interstate. How long will it take her to get to Orlando if it is 350 miles away?

Practice

4. If Jaquan has to be in Alabama by 6pm and it is noon, how fast would he have to drive to make the 800 km trip in time?