Frames of Reference is an educational film created in 1960. Professor Patterson Hume and Professor Donald Ivey from the University of Toronto are the two lecturers in the film, and are both physics experts. As such, they illustrate various physics concepts through a series of visual activities.
In the very beginning of the film, the two professors appear on camera where one of the individuals is standing on what appears to be the floor, while the other appears to be standing on the ceiling. They banter back and forth about who is on the right side. They both drop a coin to prove once and for all who is standing on the right side. It turns out, that the frame of reference in the video is misleading as it is the professor who visually appears to be standing on the ceiling is in fact the one standing right side up as the coin drops to the floor and the camera flips to reveal the truth. This scene is intended to illustrate the concept of frames of reference, which simply means the view through which an individual perceived a situation unfolding before them. In this case, the viewer’s frame of reference is misleading due to the angle of the camera.
The point of frame of reference concept is further illustrated by showing another scene. In this scene, one of the professors is sitting at a long table. Behind him is a lattice wall. The illusion is that the seat of the sitting professor is moving to the left. This is another frame of reference trick, however, because it turns out that the professor is not moving. Rather, the wall behind him is shifting right.
Next, they demonstrate the concept of frame of reference using a steel ball and an electromagnet. The electromagnet holds the steel ball until it is turned off and drops the ball. The vertical reference of the electromagnet is the focal point and we see the ball drop to the table following the vertical reference exactly. The other professor also drops the steel ball, but this time, moves the cart. The result is that the ball lands precisely in the same spot and along the same line despite the motion of the cart. It is explained to the audience that the path of the ball is actually curved and it does not fall straight down as part of the movement. Rather, you can see upon slowing down the footage of the path of the ball is actually curved. This is a visual illusion caused by one’s frame of reference. After adding a fixed frame of reference, it is clearly show that the path of the ball is curved. The professor explains that it is difficult to detect a moving frame of reference when there is not a background to fix your eye upon.
Relative motion is explained in the next experiment. In this experiment, the rate of motion within one frame of reference is compared to that of a different rate. Each professor sits at a table, the first from the previous experiment, and pass a hockey puck back and forth at the exact same rate of velocity. The camera is fixed to the table at this point, so it looks as though the puck is moving at the same rate of velocity for every pass. Next, they show the same action conducted with the camera fixed to the earth. This time, however, the puck appears to move faster when passed from the second professor to the first professor as a result of relative motion.
Next, the professors utilize the puck again which, when pushed, moves in a circle. The camera in this next scene is fixed to the earth’s frame of reference and shows the whole table where both professors sit and are rotating at the table. It is shown that the puck is indeed moving in a straight line; however, because the table and professors are moving, it appears to be the puck that is moving in circles. It is explained that a rotating frame of reference is not an inertial frame when there is a force that acts against the puck with within the rotating system which makes it move in a circle.
The last experiment shows a frame of reference situated on the globe’s equator. This experiment illustrates the acceleration of the earth in orbit as the earth rotates at its axis. In this scene, the professor explains that it is very hard to tell whether it is the earth or the stars that are moving. The professor uses a turntable and pendulum to further illustrate the inertial frame of reference.