Laws of Motion
This module introduces force, inertia, Newton's laws, momentum, impulse, friction, equilibrium and simple connected-body numericals. The focus is on KCET-speed concept clarity and formula use.
Concept Capsule
- Force is an external agency that can change the state of motion of a body.
- Inertia is the tendency of a body to resist change in its state of rest or motion.
- Newton's first law explains inertia.
- Newton's second law connects net force, mass and acceleration.
- Newton's third law states that action and reaction forces are equal and opposite, but act on different bodies.
- Linear momentum is the product of mass and velocity.
- Impulse is force multiplied by time and equals change in momentum.
- Friction opposes relative motion or tendency of relative motion.
- Limiting friction is the maximum static friction before motion begins.
- For connected bodies, apply Newton's second law to the whole system first when possible.
Which Formula Should I Use?
Use when: Net force, mass and acceleration are involved.
Watch out: Use net force, not just any one force.
Use when: Momentum is asked.
Watch out: Momentum has direction because velocity is a vector.
Use when: Force acts for a short time or impulse is asked.
Watch out: Use change in momentum, not final momentum alone.
Use when: Friction coefficient and normal reaction are given.
Watch out: On a horizontal surface, N = mg only if no other vertical force acts.
Use when: Two connected bodies move together under an external force.
Watch out: For acceleration of the system, add the masses.
Common KCET Traps
- Confusing mass and weight.
- Forgetting that action and reaction act on different bodies.
- Using individual force instead of net force in F = ma.
- Treating friction as always equal to μN without checking whether it is limiting or kinetic.
- Ignoring direction while solving force and momentum questions.
- For connected bodies, calculating acceleration using only one mass instead of total mass.
Downloads for Revision
Formula Sheet and Key Points
A Laws of Motion revision PDF will be added after the first content review.
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