Laws of Motion – Study Notes (TS EAMCET)
Why they matter
These three laws explain how objects move or stay still.
They are the foundation of all physics problems in the exam.
1. Newton’s First Law – “Law of Inertia”
| What it says | Everyday idea | Tiny example |
|---|---|---|
| An object keeps doing what it’s already doing – stay still or move straight at a constant speed – unless a net push or pull acts on it. | A book on a table stays still until you lift it; a car keeps going straight unless brakes or steering act. | If you slide a block on a smooth floor, it keeps sliding until friction slows it. |
Key point – “No net force → no change in motion.”
2. Newton’s Second Law – “F = m × a”
| What it says | Everyday idea | Tiny example |
|---|---|---|
| The push you give (force) changes an object’s speed. The bigger the mass, the harder it is to change. | Pushing a shopping cart – a heavier cart (more mass) needs a stronger push to speed up. | 10 N push on a 2 kg block → acceleration = 10 ÷ 2 = 5 m/s². |
Quick formula
Force = Mass × Acceleration
3. Newton’s Third Law – “Action = Reaction”
| What it says | Everyday idea | Tiny example |
|---|---|---|
| Every push has an equal counter‑push. | When you jump, your legs push the ground down; the ground pushes you up. | A swimmer pushes water backward → water pushes the swimmer forward. |
Takeaway – Forces always appear in pairs.
How the Laws Work Together
- Start with a situation (e.g., a ball rolling down a hill).
- Identify the forces (gravity, friction, normal force).
- Apply the first law to see if the ball would stay still or keep moving.
- Use the second law to calculate acceleration:
a = F_net / m. - Remember the third law when forces act on two objects (e.g., ball and hill).
Quick Mental Checklist for Exam Questions
| Step | What to do |
|---|---|
| 1. Read the problem carefully. | Note all given forces and masses. |
| 2. Draw a simple diagram. | Label forces, direction. |
| 3. Write the net force. | Add/subtract forces in the same direction. |
4. Use F = m × a. |
Solve for acceleration, force, or mass. |
| 5. Check units. | N, kg, m/s² – if you’re unsure, double‑check. |
| 6. Apply the third law if two objects are involved. | Remember equal and opposite forces. |
Tiny Practice Problems
| # | Question | Quick Answer |
|---|---|---|
| 1 | A 5 kg crate sits on a table. What force keeps it from sliding? | 0 N – no net horizontal force. |
| 2 | A 4 kg box is pulled with 12 N. What is its acceleration? | a = 12 ÷ 4 = 3 m/s². |
| 3 | You push a bike forward with 20 N. The bike’s mass is 20 kg. What acceleration does it get? | a = 20 ÷ 20 = 1 m/s². |
| 4 | A 1 kg ball and a 2 kg ball collide head‑on and stick together. What is their final speed if the 1 kg ball was moving at 3 m/s and the 2 kg ball was at rest? | Use momentum conservation (v_final = (m1 v1)/(m1+m2) = (1 × 3)/(1+2) = 1 m/s). |
(All numbers are tiny to keep calculations easy.)
Final Summary
- First law: Objects don’t change motion unless a net push or pull happens.
- Second law: Force equals mass times acceleration; heavier objects need more force.
- Third law: Every push has an equal counter‑push.
Remember: Draw a quick diagram → list forces → find net force → use F = m × a → check the answer.
Good luck with your TS EAMCET physics!