A catapult project turns projectile motion into something you can build, launch, measure, and improve. By changing the launch angle and spring tension, students can see how the path and range of a projectile depend on initial velocity and direction. This makes the project a strong link between hands-on engineering and physics equations.
Careful measurements help turn a classroom build into a real experiment.
Key Facts
- Horizontal velocity stays constant if air resistance is ignored: vx = v0 cos θ.
- Vertical velocity changes due to gravity: vy = v0 sin θ - gt.
- Vertical position can be modeled by y = y0 + v0 sin θ t - 1/2 gt^2.
- Horizontal range can be modeled by x = v0 cos θ t.
- For launch and landing at the same height, range is R = v0^2 sin(2θ) / g.
- If launch speed is constant and landing height is the same, the maximum range occurs at θ = 45°.
Vocabulary
- Projectile motion
- Projectile motion is the curved motion of an object moving through the air under the influence of gravity.
- Launch angle
- Launch angle is the angle between the projectile's starting velocity and the horizontal ground.
- Initial velocity
- Initial velocity is the speed and direction of the projectile at the moment it leaves the catapult.
- Range
- Range is the horizontal distance a projectile travels from launch to landing.
- Spring tension
- Spring tension is the pulling force stored in the catapult's elastic band or spring before release.
Common Mistakes to Avoid
- Changing more than one variable at a time is wrong because it makes the test unfair. Keep spring tension constant when testing angle, or keep angle constant when testing tension.
- Measuring from the wrong starting point is wrong because range must be measured from the projectile's launch position to its first landing point. Use the same reference point for every trial.
- Assuming 45° is always best is wrong because the 45° rule only applies when launch speed is constant and launch and landing heights are equal. Real catapults may change launch speed at different angles.
- Using only one trial per angle is wrong because random errors can make one launch misleading. Repeat each launch several times and use the average range.
Practice Questions
- 1 A catapult launches a ball at 8.0 m/s at an angle of 45° from ground level. Ignoring air resistance, calculate the expected range using g = 9.8 m/s^2.
- 2 A projectile is launched at 10.0 m/s at 30° from a table and lands at the same height. Find the horizontal velocity component and the vertical velocity component.
- 3 In an experiment, the 60° launch angle goes farther than the 45° launch angle even though theory predicts 45° should be best for equal launch and landing height. Explain two real-world reasons this could happen.