Practical exercise 2: DEMONSTRATION OF WEIGHTLESSNESS IN FREE FALL
You can also observe the state of weightlessness on the surface of the Earth, during free fall. If an object moves in a free fall, it moves rapidly and the fictitious force compensates for the acting gravitational force. The state of weightlessness can be observed, for example, in the following falling objects:
a) Plastic PET bottle filled with water. If a full open PET bottle falls down the bore, the liquid will not leak out. It is in a state of weightlessness and no force is exerted on the liquid, thanks to which it could leak from the bottle. The experiment can also be performed with a filled juice box. The liquid does not flow out of it through the hole in the straw during the fall either.
b) A special tool - a dynamometer with a weight suspended in a transparent box or frame. To demonstrate the state of weightlessness in free fall, it is possible to make a special device - a transparent box in which a weight is suspended on a dynamometer. The device must be made relatively durable to withstand the impact after a fall, albeit on a soft surface. At rest, the a dynamometer shows a deflection corresponding to the mass of the weight. If we let the device fall, there will be a state of weightlessness inside and the dynamometer will show zero deflection. The dynamometer will act the same when the box is thrown upwards, horizontally or obliquely. Give it a try.
Objective:
The aim of this activity is to show pupils that a state of weightlessness can also exist on the surface of the Earth, that it is not limited to outer space. On the Earth's surface, however, the duration of the state is weightlessness is limited to short periods of a maximum of a few seconds.
Instructions for the teachers:
• All listed variants of the experiment are equivalent.
• A general problem is that free fall on the Earth's surface can only be achieved for a very short time, during which the experiment can also be observed. It is appropriate to capture the implementation of the experiment with a camera with a short exposure time.
• Another problem is that the falling object must be stopped at the end of the experiment, if possible in such a way that it does not break. From this point of view, a falling PET bottle or juice box is more accessible. However, performing an experiment with a dynamometer showing zero deflection is again more convincing.
• A special tool for the demonstration of weightlessness was produced in the Czech Republic. It was just a transparent frame, inside which was a weight on a spring. We do not currently know the supplier.
• It is also worth noting that, as in the box with the weight on the spring, a state of weightlessness would arise in a falling torn elevator or in a falling cabin on one of the major attractions of the roller coaster.