Describe the motion of the object.?

Question

If a coin is thrown straight up in the air, it goes upward, reaches it's highest point and then falls back down...that's common sense but if the coin is moving upward after it is released what is the acceleration? I thought it would be increasing in the positive direction, but it's not.

Can anyone help?

thanks.

Answer 1

The acceleration is a constant downwards, at 9.8 m/s2

Don't forget acceleration is rate of change of speed.  Also Newton's law, objects in motion tend to stay in motion unless acted on by an external force (gravity in this case).

The reason the coin slows down as it goes up is because the acceleration is downwards! If there were no acceleration, it would continue to rise at a constant speed.

Another example is an auto moving at 60 mph. In order to stop you have to apply the brakes, which is a negative acceleration.

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Answer 2

For an object that doesn't travel very far away from its initial position with respect to the Earth's center of mass (like a coin being flipped straight up in the air by someone on the surface of the Earth), the magnitude of the acceleration from the Earth's gravitational pull is nearly constant at approximately 9.81 meters per second per second. This acceleration is always oriented directly toward the Earth's center of mass because gravity is a purely attractive force. For someone on the surface of the Earth, this acceleration is straight down. Another acceleration comes from air resistance, which is always pushing in the direction opposite the object is traveling; however, the air resistance this is much less than gravity in this situation.

Answer 3

That is not just common sense, that is a fact, predictable by physical laws.

When the coin leaves your hand and moves upward in positive direction, it is its velocity that is positive, not the acceleration. The acceleration due to the attraction of the earth, always pointing downward, is negative (a = -g).

Whenever the velocity and the acceleration are in opposite directions, the velocity will decrease until it is equal to 0, after that it changes the direction, pointing downward like the acceleration. The velocity becomes negative but increases in magnitude.