Frames of Reference is a short educational film created in 1960 and led by Professor Patterson Hume and Professor Donald Ivey from the University of Toronto. Throughout the film, the professors demonstrate various aspects of physics.
The film begins with the two professors on camera. One professor is standing right side up and the other upside down. They argue about which is upside down, both claiming to be on the right side. To prove their point, they drop a coin and it turns out that the professor, who appeared to be right side up, is really upside down. They make the point of frame of reference, meaning that one’s frame of reference may differ from another’s depending on their view. Because the camera was actually upside down, the viewer’s frame of reference was to associate the professor who was upside down, to be right side up. To further illustrate, they make the point that all motion is relative by having one professor sit at a table, in front of a lattice wall. While visually, it appears that the professor’s seat is moving to the left, in fact, it is the wall behind him moving to the right.
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The professor then demonstrates a steel ball being held up by an electromagnet. Once the electromagnet is turned off, the steel ball falls to the table directly along the vertical reference line (steel bar) which was holding it. The next professor conducts the same experiment; however, does so while the cart is moving at a constant velocity. This time, as the ball falls, it lands in exactly the same position despite the motion of the cart. The professor explains that the ball does not fall straight down due to the movement, however. Instead, the path of the ball, when slowed down, is clearly curved. The professor explains that this visual illusion is due to our frame of reference, which makes the ball appear, in real time, to fall straight down despite the movement. When a fixed frame of reference is added, however, you path of the ball can clearly be seen. The professor makes the point that a moving frame of reference is difficult to detect without a background and that a moving frame of reference, which is moving at a constant velocity, is the same at any rate.
The next experiment on relative motion compares the rate of motion in one frame of reference to the rate of motion in a different rate of motion. For this experiment, both professor sit at a table and pass an object (puck) back and forth at the same rate of velocity. Because the camera is fixed at the table, it appears to move at the same rate between professors. When the viewer watches from a camera fixed to the earth, the puck appears to move faster when pushed from the second professor to the first. The concept of relative motion is explained.
The ball experiment is conducted again; however, on a cart that is moving at a higher speed. This time, the ball lands in a different spot because the speed of the car continues to accelerate as the ball drops. Inertial frame is explained as the reason why the ball falls behind the bar instead of straight down, as one would assume would be the case due to gravity.
The last experiment returns us to the puck which is being pushed, but not moving straight across the table. Instead, it moves in a circle. Watching the puck in a camera fixed in the earth’s frame of reference shows that the entire table and both professors are rotating and that the puck is indeed moving in a straight line, but due to the motion of the table and the professors, the puck appears to move in a circular fashion due to the fact that the camera was fixed to the table due to the different frame of reference. When a force acts against the puck in the rotating system, it moves in a circle. As such the professors make the point that a rotating frame of reference is not an inertial frame.
The next experiment shows a frame of reference placed on the equator of a globe. This experiment shows the acceleration of the earth in orbit as the earth is rotating at its axis. The professor makes the argument that it is hard to tell whether the earth or stars are moving. A turntable is represented by the earth and the pendulum serves as the stars. In this experiment, the professor illustrates inertial frame of reference through the example of the earth and stars.
