Physical Science: Forces, Motion, and Energy
What you must understand
A force is a push or pull that can change an object's motion. Know balanced forces (no change in motion) vs. unbalanced forces (acceleration). Understand Newton's laws: an object at rest or in uniform motion stays that way unless a net force acts; force equals mass times acceleration; every action has an equal and opposite reaction. Distinguish speed (distance/time) from velocity (speed with direction) and acceleration (change in velocity over time).
For energy, know kinetic energy (energy of motion) and potential energy (stored, e.g., gravitational). Energy is conserved - it transforms between forms but is not created or destroyed. Recognize friction as a force that opposes motion and converts kinetic energy into thermal energy. Know simple machines (lever, pulley, inclined plane) trade force for distance without reducing total work.
Traps to expect
Questions often confuse mass with weight - mass is constant, weight depends on gravity. Another trap is treating balanced forces as zero motion; an object can move at constant speed with balanced forces. Watch for "energy is used up" - energy is transformed, not destroyed. Also check units and whether distance or displacement is being asked.
Worked example / rule of thumb
A car travels 150 m in 10 s. Speed = 150 ÷ 10 = 15 m/s. If it then stops in 5 s, acceleration = (0 − 15) ÷ 5 = −3 m/s², a deceleration. Rule of thumb: net force controls acceleration; energy changes form but is conserved.
Key ideas
- Balanced vs. unbalanced forces
- Newton's three laws of motion
- Speed, velocity, and acceleration
- Kinetic vs. potential energy and conservation
- Friction and simple machines