Question

Describe Galileo's experiment on inclined planes.

Accepted Answer

Through the observations of the motion of objects on an inclined plane, Galileo deduced that objects move with a constant speed when no force acts on them. He observed that when a marble is made to roll down an inclined plane- $l$ (as indicated in the following figure), its velocity increases in magnitude.

Here, the marble rolls down under an unbalanced force due to gravity. That is why its velocity is increasing to attain a definite velocity at the bottom of the inclined plane. However, the velocity of the marble decreases when it climbs up the other inclined plane- $Il$ as shown in the following figure.

Thus, in the case of planes that slope downwards, there is present a cause of acceleration while on planes sloping upwards there is acceleration opposite to the direction of motion.

In the second set of experiments, Galileo combined two inclined planes $I$ and $Il$ together facing each other and highly polished to minimise the friction. He argued that when a marble is made to roll down the inclined plane $I$ from a height ‘ $h$ ’, it would rise up the plane- $Il$ to almost the same height as shown in the following figure.

He then decreased the inclination or slope of plane- $I$ and repeated the experiment. This time the marble had to travel a longer distance on the plane $Il$ to reach almost the same height. If the friction were totally eliminated, the final height reached on the plane- $Il$ would be equal to the initial height in plane- $l$ , as a limiting case. If the slope of plane- $Il$ is made zero (as indicated in the above figure) that means horizontal, the marble should move forever because it will never attain the initial height. The unbalanced forces on the marble are zero in this situation. In actual practice, it is difficult to achieve a zero unbalanced force. Thus, in practice, the marble comes to rest after travelling some distance.

Describe Galileo's experiment on inclined planes.

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