Final answer:
The demonstration using a rubber sheet and a tennis ball illustrates the concept of spacetime curvature as described by Einstein's general theory of relativity, with the ball creating a depression that represents gravitational effects on objects passing nearby.
Step-by-step explanation:
In a demonstration where a student places a tennis ball on a stretched rubber sheet, the concept being illustrated is the curving of spacetime due to the presence of matter. This is a two-dimensional analogy used to model Einstein's general theory of relativity, which posits that matter curves the fabric of spacetime and this curvature affects the motion of objects. The rubber sheet represents spacetime and the tennis ball represents a mass like a planet or star whose gravity causes a depression in spacetime. When objects such as other masses or light rays pass near the depression, their paths are curved, which is akin to what we observe with gravity in our three-dimensional world.
To provide evidence for this theory, one can point to astronomical observations where light rays from distant stars are bent when they pass near massive objects, a phenomenon known as gravitational lensing. This effect was first observed during a solar eclipse in 1919 and confirmed Einstein's prediction that light would be deflected by gravity, offering strong support for the general theory of relativity. Therefore, the demonstration with a rubber sheet and tennis ball not only offers a simple way to visualize complex principles of physics, but it is also supported by empirical evidence from observations in the cosmos.