To apply Newton's second law, sometimes we first need to find acceleration: = ???? ???? ???? ???? ???? is the change in an object's velocity. Velocity can have a positive or negative direction (negative signs need to be considered when calculating change in velocity and acceleration). Quantity Variable or Abbreviation Unit Unit Symbol acceleration a meters per second per second m/s2 final velocity m/s u m/s t s Tamara is riding a bike. The starting velocity of the bike is 3 meters/second. After 10 seconds, the velocity increases to 5 meters/second. What's the bike's acceleration? ???? = ? ???? = m/s ???? = m/s ???? = s ???? = ???? ???? ???? = 5 3 10 m/s2 = m/s2 When we analyze collisions, objects are moving in two directions. We assign one direction to be _____________ and the other to be _______________. The object's velocity is positive or negative. An object's acceleration is also positive or negative. But this acceleration isn't the _________________ of motion. Instead, ______________ and ______________ acceleration show the direction of _________. speeding up acceleration = +a slowing down acceleration = +a The image shows force exerted in only the positive negative direction, which results in positive acceleration. _____________ _____________________ can refer to an object moving in the positive direction and _______________ ____. It can also refer to an object moving in the negative direction and ________________ ________