Gravitational Forces

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A freely falling object is an object that is under the influence of gravity. There are two important characteristics of motion that are valid for free falling objects:

1. free falling objects do not encounter air resistance;
2. all free-falling objects (on Earth) accelerate downward at 9.8 m/s/s (often approximately 10 m/s/s).

This acceleration can be visualized by a bar trace or dot plot of the motion of free-falling objects. The dot diagram below shows the position of the object at regular time intervals – for example, every 0.1 seconds. The fact that the distance the object travels at each time interval increases is a sure sign that the ball is accelerating as it falls downward.

Source: http://www.physicsclassroom.com/Class/1DKin/U1L5a1.gif

The cause of free fall is the gravitational force that gives the falling body gravitational acceleration. However, on every planet the gravitational acceleration is different. Therefore, free fall is also different on each planet. The greater the gravitational acceleration on a planet, the faster and with greater speed the bodies will impact the surface. The Earth and the Moon have different masses and different sizes. Therefore, their surface has different gravitational acceleration.

Questions and tasks to be performed

1. Familiarize yourself with the graphs and tables given in Excel.

To download: Worksheet Gravity tables

2. Solve the problems using the data from the tables and graphs given.

Table 1. and graph 1. show the free fall velocity of a body for a given time on Earth and on the Moon.

On the horizontal axis of the graph, the time is plotted in 0.1 second intervals. On the vertical axis is the velocity the body reaches during free fall. In blue is shown the fall of the body on the surface of the Earth. In orange is the fall of the body on the surface of the Moon.

Table 1.

А. Answer the questions:

1. How long was the body observed to fall?
2. Was the body at rest at the initial moment?
3. Does the speed of the falling body change during the fall?
4. In which fall did the body reach a greater velocity – the fall on the surface of the Earth or on the surface of the Moon?
5. Compare the velocity of the body on the surface of the Earth after 0.6 s with the velocity of the body in the same time on the surface of the Moon.

Table 2. and graph 2. show the distance traveled by the body during free fall. The fall of the body on the surface of the Earth is shown in blue, the fall on the surface of the Moon in orange. On the horizontal axis of the graph, the time is plotted in 0.1 second intervals. On the vertical axis is the distance traveled by the body during its free fall.

Table 2.

В. Answer the questions based on the data in Table 2. and Chart 2:

1. What distance did the body travel on the surface of the Earth in the first tenth of a second?
2. What distance did the body travel on the surface of the Earth in the second tenth of a second?
3. What distance did the body travel on the surface of the Earth in the third tenth of a second?
4. Does a body travel the same path every second as it falls on the surface of the Earth?
5. Compare the distance travelled during the fall to the surface of the Earth and the surface of the Moon in the same time.
6. How long does it take a body to travel more than 20 cm on the surface of the Moon?