CHAPTER 2 Distance vs Displacement Distance How far

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 20 m/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 1 st 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?