# Energy & Work — ACT Science
Energy concepts appear in many ACT Science passages, from roller-coaster experiments to heating and cooling data. Understanding kinetic energy, potential energy, and energy conservation helps you interpret results correctly.
Key Concepts
Types of Energy
- Kinetic Energy (KE): energy of motion. Faster → more KE. Heavier → more KE.
- Potential Energy (PE): stored energy. Higher position → more gravitational PE. Compressed spring → elastic PE.
- Thermal Energy: related to temperature; heat flows from hot to cold.
Conservation of Energy
Energy cannot be created or destroyed — it is transformed from one form to another.
- A ball dropped from height: PE converts to KE.
- A pendulum: KE and PE trade back and forth.
- Energy "lost" usually means converted to thermal energy (friction/heat).
Work
Work is done when a force moves an object. More force or more distance → more work.
ACT-Relevant Patterns
- As height increases, gravitational PE increases.
- As speed increases, KE increases (KE depends on speed squared).
- If friction is present, total mechanical energy decreases over time.
Worked Example
Passage summary: A ball rolls down a track. Height and speed are measured at several points.
| Point | Height (m) | Speed (m/s) |
|---|---|---|
| A | 5.0 | 0 |
| B | 3.0 | 6.3 |
| C | 1.0 | 8.9 |
| D | 0 | 9.9 |
Q: Which statement is best supported?
A: As height decreases, speed increases — PE is converting to KE, consistent with conservation of energy.
Practice Questions
1. A pendulum swings from its highest point to the lowest. What energy transformation occurs?
Gravitational PE is converted to KE.
2. Two identical balls are rolled down the same hill, but one hill has more friction. Which ball has more speed at the bottom?
The ball on the less-frictiony surface is faster — less energy is lost to heat.
3. If an object's speed doubles, by what factor does its kinetic energy change?
KE quadruples (factor of 4), since KE depends on .
Want to check your answers and get step-by-step solutions?
Summary
- Energy is conserved: PE + KE + thermal = constant.
- PE increases with height; KE increases with speed (squared).
- Friction converts mechanical energy to thermal energy.
- On the ACT, look for energy trends in tables and graphs.