# Gravity & Projectile Motion — ACT Science
Gravity and projectile motion experiments are common ACT Science passage topics. You may need to read tables showing how launch angle, speed, or height affects a projectile's range or time in the air.
Key Concepts
Gravity
- Near Earth's surface, all objects accelerate downward at about .
- Without air resistance, mass doesn't affect falling speed.
- Gravity acts on projectiles throughout their flight.
Free Fall
- An object dropped from rest speeds up as it falls.
- An object thrown upward slows down, stops momentarily, then speeds up downward.
Projectile Motion
- A projectile has two independent components of motion:
- Horizontal: constant speed (no acceleration, ignoring air resistance).
- Vertical: accelerated by gravity.
- The path is a parabola.
- Launch angle of 45° gives maximum range (on flat ground, no air resistance).
- Complementary angles (e.g., 30° and 60°) give the same range.
Key Trends to Recognize
- Greater launch speed → greater range and height.
- Greater launch angle (up to 45°) → greater range; beyond 45° → range decreases.
- Greater height → longer time in the air.
Worked Example
Passage summary: A ball launcher fires at various angles with the same speed.
| Angle (°) | Range (m) | Max Height (m) |
|---|---|---|
| 15 | 25.0 | 3.4 |
| 30 | 43.3 | 12.5 |
| 45 | 50.0 | 25.0 |
| 60 | 43.3 | 37.5 |
| 75 | 25.0 | 46.6 |
Q: At what angle is the range maximized?
A: 45°. Also note that 30° and 60° give the same range, as do 15° and 75°.
Practice Questions
1. Two balls are launched at the same speed — one at 20° and one at 70°. Which goes farther?
They travel the same horizontal distance (complementary angles).
2. A ball is thrown straight up. At the very top of its path, what is its velocity? What is its acceleration?
Velocity = 0. Acceleration = 9.8 m/s² downward (gravity never stops).
3. If you double the launch speed (same angle), what happens to the range?
The range quadruples (range is proportional to speed squared).
Want to check your answers and get step-by-step solutions?
Summary
- Gravity accelerates all objects equally ( down).
- Projectile motion: horizontal (constant speed) + vertical (accelerated by gravity).
- 45° launch angle maximizes range; complementary angles give equal range.
- On the ACT, look for trends in launch angle, speed, and resulting range/height.