1. Mass and Motion

2. Mass  Matter has substance. Solids, liquids or gasesSolids, liquids or gases Subatomic particlesSubatomic particles Planets and starsPlanets and stars  Weight is not mass, but mass can have weight.  Mass measures the amount of matter in an object.

3. Mass Units  Mass is measured in kilograms. 1 kg = 1000 g 1 atomic mass unit (about the mass of one hydrogen atom) = 1.66 x 10 -27 kg  Pounds measure weight (a force) not mass. © R. Rathe, NIST

4. Force and Acceleration  With force there is acceleration.  The amount of acceleration depends on the mass.  Mass is a scalar. Mass times a vector gives another vector.Mass times a vector gives another vector. The direction of the force and acceleration are the same.The direction of the force and acceleration are the same.

5. Force Units  Force is mass times acceleration.  The dimensions of force are M(L/T 2 ).  In SI units a newton (N) = 1 kg m / s 2.

6. Second Law: Law of Acceleration 2 The change in motion is proportional to the net force and the change is made in the same direction as the net force.  Net force gives rise to acceleration.  Force = mass x acceleration (Newton’s second law). Rocket: has mass Force: becomes acceleration Initial velocity Final velocity: changed by the force

7. Vector Force  A 1000 kg satellite in space is moving at 5.0 km/s when a rocket fires with a thrust of 5.0 x 10 3 N at 60° to the direction of motion.  The rocket fires for 1 minute. Where does it move after firing?  Identify the quantities in the problem: Mass, m = 1000 kg Initial velocity, v 0 = 5 x 10 3 m/s Force, F = 5 x 10 3 N at 60° Time, t = 1 min = 60 s  Force and velocity are vectors Pick x in the direction of initial motion: v x = v 0. F x = F cos  F y = F sin  x  = 60  F = 5000 N

8. Change in Velocity  A 1000 kg satellite in space is moving at 5.0 km/s when a rocket fires with a thrust of 5.0 x 10 3 N at 60° to the direction of motion.  The rocket fires for 1 minute. Where does it move after firing?  The force gives acceleration. a x = F x /m = (F/m) cos  a y = F y /m = (F/m) sin   The change in velocity is due to this acceleration. v x = v 0 + a x  t = v 0 + (F t / m) cos  v y = a y  t = (F t / m) sin   The final velocity is v x = 5200 m/s = 5.2 km/s v y = 260 m/s = 0.26 km/s. next v v0v0