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Explanation of the Effect of Gravity on Sideways Motion - Succeed in Understanding Physics. Also refer to physical science, Earth, parallel, propel, throw, ball, gun, shoot, bullet, rate, acceleration, fall, Ron Kurtus, School for Champions. Copyright © Restrictions
Effect of Gravity on Sideways Motion
by Ron Kurtus (28 August 2009)
When an object is moving sideways or parallel to the Earth's surface at a constant velocity, the effect of gravity on the object is independent of its lateral movement. In other words, an object moving sideways will fall at the same rate as one that is simply dropped.
An exception to this rule is if the object moves so fast or far that the curvature of the Earth comes into play during its fall to the ground.
Questions you may have include:
- What is the pull of gravity for a moving object?
- What rate do objects moving sideways and stationary fall at?
- When happens when you shoot a gun parallel to the ground?
This lesson will answer those questions. There is a mini-quiz near the end of the lesson.
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Pull of gravity same for moving object
Since the Earth is a sphere with a circumference of approximately 40,000 km or 25,000 mi, the ground can be considered level or flat—not counting hills and valleys—for short distances of several kilometers or several miles.
Gravity acts on objects in a direction that is perpendicular to level ground. This means that, if an object is moving parallel to the ground, the force of gravity is only pulling on the object in a downward direction. The force is not affected by sideways motion and simply pulls the object down at the same rate as if it was stationary.
Pull of gravity downward is the same for moving and stationary objects
Hits ground at same time
If you would throw an object exactly parallel to the Earth's surface, the sideways motion of the object would have no effect on how gravity acts on it. In other words, the object would drop at the same rate as an object dropped from the identical height. The time it would take either object to hit the ground would be the same.
Ball thrown sideways falls at the same rate as dropped ball
Simple experiment
You can try a simple experiment to verify this phenomenon. Place a coin on the edge of a table or desk and hold another coin at the same height. With one hand flick the coin on the table across the room. At the same time, drop the other coin. You will hear that they hit the floor at just about the same time.
Equations for falling object hold
All the equations for velocity, distance and time for a falling object would apply to the object thrown sideways in the direction toward the ground. (See Gravity Equations for Falling Objects for information on equations.)
Shooting a bullet
If you would shoot a bullet from a gun exactly parallel to the Earth's surface, the motion of the bullet would have no effect on how gravity acts on the bullet. In other words, the bullet would drop at the same rate as a stationary object.
Dropped bullet and shot bullet hit the ground at the same time
Many people don't believe that if you held a rifle or handgun parallel to the ground and at the same time you shot the bullet, you dropped another bullet from the same height, both bullets would both hit the ground at the same time. However, it is a fact.
Exception
An exception to this phenomenon would be if the bullet or object was able to travel so many miles or kilometers that the curvature of the Earth came into play. In such a situation, the bullet would take slightly longer to hit the ground, because the distance to the ground was greater due to the Earth's curvature.
Summary
An object moving parallel to the Earth's surface at a constant velocity falls at the same rate as one that is simply dropped. An exception to this rule is if the object travels a great enough distance that the curvature of the Earth comes into play during its fall to the ground.
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Resources
The following resources provide information on this subject:
Websites
Acceleration due to Gravity Calculations - from Western Washington University
Gravitation and Gravity Resources
Books
Top-rated
books on Simple Gravity Science
Top-rated
books on Advanced Gravity Physics
Mini-quiz to check your understanding
If you got all three correct, you are on your way to becoming a Champion in Physics. If you had problems, you had better look over the material again.
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Effect of Gravity on Sideways Motion