Motion

Bell Work

• How do you feel when you are standing on a stopped bus and then the bus begins to move? Why?

Objectives

• Define motion.

• Calculate the speed of a moving object.

• Distinguish between velocity and acceleration.

Motion

• The change in position of an object as compared with a reference point.

Reference Point

• Reference point: a place or object used for comparison to determine if something is in motion.

• To measure movement, some point must be considered as nonmoving.

• Earth is the most common frame of reference.

Question

• Car A is going 45 mph in the left lane. Car B is going 45 mph in the right lane directly along side car A. Is car B in motion relative to car A? Explain.

Not All Motion Is the Same

• All motion is not the same.

Activity• Differentiate between the

motion of a baseball and a jet.

Distance

• The length of the actual path traveled by an object.

• A car travels 50 km.

• A baseball travels 60 feet and 6 inches.

Speed• The distance an object travels

in a given amount of time.

• A car travels 50 km in one hour.

• A baseball travels 85 miles per hour.

Calculating Speed

• The formula s = d/t is used to calculate speed.

• s is speed, d is distance, and t is time.

Activity

1. If a runner runs 100 meters in 50 seconds, what is his speed in meters per second?

2. If the same runner runs the next 100 meters in 60 seconds, what is his average speed for the entire distance?

Speed

• Instantaneous Speed - the speed of an object at one instant of time.

• Average Speed – the overall rate of speed at which an object moves; calculated by dividing the total distance an object travels by the total time.

Velocity

• Speed in a definite directiondefinite direction.

• 65 km/hour describes speed.

• 65 km/hour north describes velocity.

Velocity

• Two objects can have the same speed but have different velocities.

• 70 mph north and 70 mph south.

Questions

1. A ball moves 20 meters in 5 seconds. What does this tell you about the motion of the ball?

a. Direction and size b. Speed and weight

c. Distance and time d. Force and direction

2. What is the speed of the ball described in the questions above?

Acceleration

• Acceleration is a change in velocity in a period of time.

Which of the Following Are Examples of Acceleration?

• A car stops at a stop light.

• A car goes from 0 to 45 mph.

• A car races around an oval track at a constant speed.

Acceleration

• Acceleration is any change (speed or direction) in an objects motion.

• Acceleration can be negative.

Acceleration of Objects in Free Fall

• The acceleration of an object in free fall on earth is 9.8 m/s.

• This means that in each second the speed of the object will increase by 9.8 m/s.

Calculating Acceleration

• Acceleration = final speed – initial speed• time

• The unit of acceleration is m/s²

Calculating Acceleration

• What would be the speed of an object in free fall after 3 seconds?

• How fast would the object be traveling after 5 seconds?

• How fast would the object be traveling after 10 seconds?

Review

• What is the difference between speed and velocity?

• A train travels 85 km in 1.5 hours. What is the speed of the train?

Review

• What is the difference between velocity and acceleration?

• If the moon travels at a constant speed around the earth, would the moon’s velocity also be constant? Why?