Evans SPH 4U1

Physics Grade 12

Unit 3: Circular Motion

Note 2: Apparent Weight


Reference Chapter 3.2 & Section page 148

Non-inertial Frame of Reference: An accelerating frame of reference where the Law of Inertia (Newton's 1st Law) does not hold.

Apparent Weight: The net force on an accelerating object in its non-inertial frame of reference (i.e. If you are in an elevator accelerating downward the normal force pushing up on you is less so your apparent weight is less).

Centrifuge: rapidly-rotating object used to separate substances according to their densities.


~ Throw a ball, throw it further, fire a cannon, keep extending the reach and what will the trajectory be?

~ Where is the space shuttle in relation to earth? Why do astronauts feel weightless?
(often referred to with misleading terms such as free fall, zero gravity, microgravity). Note: The absence of forces against astronauts' muscles cause the muscles to become smaller and bones to become brittle.


Centrifugal Force: Do you weigh more at the equator or at the poles? ~ demo on globe

Coriolis Force: ~demo pendulum at north pole on globe
 Example 1:

A 58 kg test pilot flies her plane in a vertical circular loop of radius 640m at a constant speed of 140 m/s. Determine the force the seat exerts on her::

a) At the bottom of the loop Answer: 2.3 x 103 N [Up]

b) At the top of the loop Answer: 1.2 x 103 N [down]

c) Calculate the minimum speed that will result in the pilot feeling "weightless" at the top of the loop. Answer: 7.9 x 101  m/s


Example 2:

A pilot having a mass of 8.0 x 10 kg, executes a vertical loop of radius 6.0 x 10 2 m in his plane.  What force does the pilot exert on his seat at the bottom of the vertical loop if his speed is 1.8x 10 2 m/s? Answer: The seat exerts a force of 5.1 x 103 N [up] on the pilot so therefore the pilot exerts a force of 5.1 x 10 3 N [down] on the seat.


Example 3:

If the earth's radius is approx. 6100 km find the orbital velocity that the shuttle would have.

Answer: 27 835 km/h