Exploring Accelerated Motion

Tossing ball above motion detector

- At rest or moving with constant velocity: acceleration = 0 (Newton’s first law)

Tossed ball:
- ball starts with high speed
- slows down as moves up
- as turns around velocity moves through zero but the ball does not stop
- speeds up as falls back down
*(acceleration is constant due to constant force on the ball by the Earth)

Note that the sign of the acceleration is arbitrary; depends on decision of which is the positive direction:

• if “up” is the positive direction, acceleration is negative throughout the motion – pull is always ‘down’ toward the center of the earth)
• if “down” is positive direction, acceleration is positive throughout the motion – pull is always ‘down’ toward the center of the earth)