Types of Forces

• Force as a push or pull that can change speed, direction, or shape.
• Contact forces — friction and muscular force (need touching).
• Non-contact forces — magnetic, electrostatic, and gravitational (act at a distance).
• How to identify forces in everyday situations (walking, lifting, magnets, charged comb).

1. Force (F) — interaction changing motion or deformation; SI unit newton (N).
2. Contact forces — friction (opposes motion), muscular force (muscles of humans/animals).
3. Non-contact forces — gravity (Earth's pull), magnetic force (magnet–iron), electrostatic force (charged objects).
4. Effects of force — start/stop motion, change direction, change shape (spring, rubber ball).
5. Diagram (text) — arrow labelled F shows direction and magnitude of applied force.
6. Real world — goalkeeper stops ball (contact force); Moon orbiting Earth (gravity); fridge magnet (magnetic).

Identifying forces when pushing a box on rough floor

Step 1 — Muscular force: you push the box forward.
Step 2 — Friction: floor pushes opposite to motion (contact).
Step 3 — Gravity: Earth pulls box downward (non-contact).
Step 4 — Normal force: floor pushes up balancing weight (contact).
Conclusion: Multiple forces act; net force decides motion.

• Calling weight and mass the same (mass in kg; weight is force in N).
• Thinking friction always wastes energy (helps walking and braking).
• Assuming non-contact forces need air (gravity works in vacuum).
• Forgetting force is a vector (has direction).

• Name two contact and two non-contact forces.
• What happens when equal and opposite forces act on a book at rest?
• Give one example where force changes only shape.

Open the Practice tab for graded questions on Types of Forces.