Exploring Compound Motion

3.3 based on 6 ratings

Updated on Feb 05, 2012

Grade Level: 6th - 8th; Type: Physics


Compound motion occurs when two forces act on the same object. This science project explores how compound motion works.

Research Question:

Is the force of gravity affected by a horizontal force?

If you drop a ball, the force of gravity makes it hit the ground. If you throw a ball, two forces are working on the ball – gravity, and the horizontal force from your throw. Which ball do you think would hit the ground first? Use this science project to find out.


  • Ruler
  • 2 pennies

Experimental Procedure:

  1. Place a ruler so that it is halfway on the table, perpendicular to the side of the table.
  2. Rest your left finger on the ruler right where it hits the edge of the table.
  3. Use your right finger to push one end of the ruler sideways so that it is now on a diagonal with the table.
  4. Place one penny at the end of the ruler that is off the table.
  5. Place the other penny on the table between the other end of the ruler and the edge of the table.
  6. Strike the ruler in the same directly as you did before, but suddenly. This will make both pennies drop to the floor at the same time. One will drop straight down, and the other will shoot out horizontally as it falls.
  7. Watch the pennies to see which one hits the ground first. Repeat the experiment several times to check your data. What does that tell you about the effect of horizontal movement on gravitational force?

Terms/Concepts: Gravity; Forces; Compound motion; How quickly do objects fall?


  • Goal! Science Projects with Soccer, by Madeline Goodstein. Pp 31-33.

Keren Perles has worked as an educational writer, editor, teacher, and tutor of all ages. Her experience spans the subject areas, from science and math, to English and the Hebrew language.

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