Projectile Motion (Chelsey Traylor)

Author

Chelsey Traylor, 8th grade Physical Science Teacher

Principles

A dropped ball and thrown ball will hit the ground at the same time (simultaneously)

Standards

8.2.d. Students know how to identify separately the two or more forces acting on a single static object including gravity, elastic forces, and friction.

Materials needed

projectile demonstration apparatus, marbles or steel ball bearings

Procedure

1. Attach the apparatus to the lab work bench.

2. Place each marble on the demonstration apparatus.

3. Pull the lever and observe as one ball is dropped and the other ball is shot forward.

4. Observe when each ball hits the ground.

Explanation

When the two are released, the fact that one ball is being propelled forward has nothing to do with the fact that it is being accelerated downward. The two directions are perpendicular to each other, and hence have no effect on each other. The two balls will hit the floor at exactly the same time. They will hit the ground at the same time because while they will have different velocities over all, they will at all times have the same vertical velocity. And its that velocity which determines when they hit the ground. All objects accelerate to the ground at 9.8 m/s².

Questions

1. At what rate did the ball thrown accelerate at and the ball dropped accelerate at due to gravity? (Answer - 9.8 m/s²)

2. Explain how shooting a bullet from a gun and dropping a bullet will have the same results as you saw in the demonstration. (Answer: The reason is that the force of gravity is a constant, so the bullet will be pulled down vertically at the same speed, regardless of its horizontal speed.)

3. Question

Everyday examples of the principles illustrated

A ball thrown from one person to another in basketball, baseball, or football. When anybody is playing sports with a ball, the sports ball will curve in an arc and hit the ground at the same time the ball is dropped from the same height.

Photos

Movies

References

Horizontal Motion Apparatus - Physics Demonstrations