Is Mass the Same Thing as Weight?

1. Is Mass the Same Thing as Weight? • mass – the amount of matter in an object • weight – a measurement of the force which acts upon an object When in “free-fall,” you are weightless!!

2. Forces • Forces change the motion of objects – cause acceleration. • momentum – the (mass x velocity) of an object p = mv [kg m/s] • force – anything that can cause a change in an object’s momentum F = D(mv) = mDv = ma [kg m/s2 =N]

3. Escape velocity ! • Can an object escape the gravitational attraction of the Earth? • Does it have enough kinetic energy to overcome the gravitational potential energy of the Earth? mgh I ½ mv2 ????

4. Depending on its initial velocity, the cannonball will either fall to Earth, continually free-fall (orbit), or escape the force of Earth’s gravity.

5. Homework #4 • A set of keys is dropped from the top of the Empire State building in New York. How fast will they be going when they hit a poor tourist on the ground 9 seconds later? • How tall is the Empire State Building? • An astronaut drops his set of keys from the same height as the Empire State Building on the Moon (1/6th the gravity of Earth), how fast is it going when it hits the Lunar surface?

6. Angular Momentum • angular momentum – the momentum involved in spinning /circling = massnvelocitynradius • torque – anything that can cause a change in an object’s angular momentum (twisting force) massnaccelerationnradius

7. v m r An object traveling at constant speed v in a circle of radius r experiences acceleration given by v2/r a = v2/r F = m v2/r