Shoot the Monkey

This classic demonstration shows that the horizontal and vertical components of a projectile’s motion are independent. A projectile fired from a cannon hits a monkey that drops from a tree at the same instant, because both fall with the same vertical acceleration due to gravity.

1. Suspend a stuffed monkey (with a metal plate or shield attached) from an electromagnet.
2. Aim a spring-powered cannon directly at the monkey while it hangs.
3. As the cannon fires a steel ball, the circuit releases the electromagnet, causing the monkey to drop at the same moment.
4. Observe that the ball follows a parabolic path and strikes the monkey in midair.
5. Emphasize that the hit occurs regardless of projectile speed or distance, because both objects fall with the same gravitational acceleration.

Shoot the falling target demo - Rhett Allain:

📄 Shoot the Monkey - Harvard Natural Sciences Lecture Demonstrations: https://sciencedemonstrations.fas.harvard.edu/presentations/shoot-monkey

• Adjust the cannon’s angle or spring compression to change the projectile’s speed and collision height.
• Vary the monkey’s starting height to demonstrate collisions at different points in space.
• Replace the monkey with another target object to keep the concept but reduce theatrical effect.

• Never stand in front of the loaded cannon.
• Secure the cannon firmly to prevent movement when firing.
• Use a shield or barrier to protect the audience from stray projectiles or ricochets.
• Practice loading and firing carefully; the spring mechanism requires significant force.
• Ensure the target is padded or reinforced to withstand repeated impacts.

• Why does the projectile always hit the monkey, regardless of speed or angle? (Because both the projectile and monkey fall with the same acceleration due to gravity.)
• What would happen if there were no gravity? (The monkey would not fall, and the projectile would miss.)
• How does this demonstration disprove the Aristotelian view of motion? (It shows that motion is the combination of independent horizontal and vertical components, not a mix of “violent” and “natural” motion.)