Forces & Motion
How forces make things move, stop, or change direction
A force is a push or a pull. Forces can make objects start moving, stop, speed up, slow down, or change direction.
Newton's Laws of Motion:
1st Law (Inertia): An object stays still or keeps moving at constant speed unless a force acts on it. A parked car won't move by itself — you need to push it or start the engine.
2nd Law: Force = Mass × Acceleration (F = ma). A heavier object needs more force to accelerate. That's why it's harder to push a loaded truck than an empty one.
3rd Law: For every action, there is an equal and opposite reaction. When you jump, your feet push down on the ground, and the ground pushes you up.
Types of Forces:
Resultant Force: The single force that has the same effect as all forces combined. If forces are balanced (resultant = 0), the object stays at constant velocity. If unbalanced, it accelerates.
Key Points to Remember
- 1Force = Mass × Acceleration (F = ma)
- 2Weight = mass × gravitational field strength (W = mg)
- 3Balanced forces = constant velocity or stationary
- 4Unbalanced forces cause acceleration
Pakistan Example
Cricket Ball Bowling
When Shaheen Afridi bowls at 150 km/h, he applies a massive force to the cricket ball (F = ma). The ball has a small mass (~160g), so even a moderate force produces huge acceleration. Once released, air resistance and gravity act on the ball — that's why fast bowlers get swing! The ball's curved path is because air flows differently over the seam, creating an unbalanced force sideways.