1. Frames of Reference Caution: Your brain is about to be twisted! KL phys 09 Science is nothing but perception. Plato Plato There is no fixed physical reality, no single perception of the world, just numerous ways of interpreting world views as dictated by one's nervous system and the specific environment of our planetary existence. Deepak Chopra There are children playing in the streets who could solve some of my top problems in physics, because they have modes of sensory perception that I lost long ago. J. Robert Oppenheimer J. Robert Oppenheimer

2. Consider this… You are sitting in the passenger seat of your friend’s car. The speedometer reads 30 mph. How fast are you moving? How fast is your friend moving? You pass a friend standing on the corner. How fast is he moving?

3. The reality is that your motion affects what is seen. Motion is relative!

4. Your (the passenger) point of view You are sitting in the passenger seat of your friend’s car. The speedometer reads 30 mph. How fast are you moving? v=0 mph How fast is your friend moving? v=0mph You pass a friend standing on the corner. How fast is he moving? v=-30 mph ( 30 mph backwards)

5. The driver’s point of view You are sitting in the passenger seat of your friend’s car. The speedometer reads 30 mph. How fast are you moving? v=0 mph How fast is your friend moving? v=0 mph You pass a friend standing on the corner. How fast is he moving? v = -30 mph (30 mph backwards)

6. Your friend on the corner’s point of view You are sitting in the passenger seat of your friend’s car. The speedometer reads 30 mph. How fast are you moving? v=30 mph How fast is your friend moving? v=30 mph You pass a friend standing on the corner. How fast is he moving? v = 0 mph

7. From the point of view of a car moving along at 20 mph as you pass the slow poke. You are sitting in the passenger seat of your friend’s car. The speedometer in your friend’s car reads 30 mph. How fast are you moving? v=0 mph How fast is your friend moving? v=0 mph How fast is the car you passed moving ? v=-10 mph For the 2 cars moving in the same direction the relative velocity is found by subtraction and the +/- depends on the reference point.

8. From the point of view of a car coming head on towards you at 20 mph You are sitting in the passenger seat of your friend’s car. The speedometer in your friend’s car reads 30 mph. How fast are you moving? v=0 mph How fast is your friend moving? v=0 mph How fast is the car coming towards you moving ? v= -50 mph For the 2 cars moving in the opposite directions the relative velocity is found by addition and the +/- depends on the motion towards or away from a reference point.

9. Example: Your friend tosses a ball upwards while riding in a car Does the FBD change if the ball is on its way towards the ceiling? at the top of its trajectory? on its way back down? moving sideways? Weight

10. Example: Your friend tosses a ball upwards while riding in a car What path do you see? If you are at rest (standing on the corner) and the ball moves sideways. If you are in the car with the ball moving together. Weight

11. Frames of Reference Inertial – Objects obey the law of inertia. Constant velocity (Constant speed, straight line) Non-inertial Explanations cause you to create “fictitious” forces because you want to believe Newton’s 1 st law. Accelerated motion What you think is true is exactly opposite what is truly happening.