CHAPTER 2

Distance vs. Displacement

• Distance:• How far an object has

moved• I ran 10 meters north

and 30 meters south. How far did I run?

• Displacement:• How far the object

moved from the starting point

• What is my displacement in the previous problem?

Motion

• Distance- how far object moved

• Displacement- distance and direction the object moved from starting location

• Speed = distance / time (Don’t forget units)

• Ex: 5 m/s

Speed

• You travel 10 meters in 2 seconds. What was your speed?

• Your speed is 100 km/h and you’ve been driving for 5 hours. How far have you driven?

Average vs. Instantaneous

• Average speed = total d / total t• Instantaneous speed = speed at that given

second

Trickier problem

• Sound travels at 330 m/s. If a lightning bolt hits the ground 1 km away from you, how long will it take for the sound to reach you?

Speed vs. Velocity

• Speed = d / t• Velocity = speed of

object and direction of its motion

Acceleration

• Change in object’s velocity (speed and direction of motion)

• Increasing speed =positive acceleration• Decreasing speed = negative acceleration• Acceleration = change velocity / time• Acceleration = (Vf – Vi) / t• Don’t forget units!• Ex: 5 m/s^2• Gravitational acceleration 9.8 m/s^2

Acceleration

• A jet airliner starts at rest at the end of the runway and reaches a speed of 300 m/s in 20 seconds. Calculate the acceleration.

Acceleration again

• A skateboarder is moving at a speed of 20m/s and comes to a stop in 2 seconds. Calculate the acceleration.

Force

• Push or pull on an object

• Gravity is a basic force

• Closer objects are together, the grav force between them increases

Balanced Force

• Net force = 0• Same force in

opposite directions cancel each other out

• No movement

Unbalanced Force

• Unequal forces in opposite directions

• Movement occurs • Net force = # in one

direction• Centripetal force =

unbalanced force, with an object accelerating towards the center

Inertia

• Tendency of an object to resist a change in its motion

• Newton’s 1st Law of Motion: an object moving at a constant velocity or at rest will remain that way unless it is acted upon by a force

• Why should we wear seatbelts?