Second Law of Motion Bigger the push, quicker the motion.

Everyday Push

Person pushing grocery cart

Push Harder = Faster Cart

Concrete example: A gentle push moves the grocery cart slowly.

Observation: A stronger push speeds it up more—greater force gives greater acceleration.

Key Points:

  • Push = force acting on the cart.
  • Acceleration is the change in speed.
  • Double the push ≈ double the acceleration. What happens to the cart?

Momentum

Momentum

Momentum \(p\) is the quantity of motion an object has. It equals mass multiplied by velocity: \(p = m \times v\). Heavier or faster objects have greater momentum and are harder to stop.

Term introduction – your first look at momentum.

Newton’s 2nd Law

\[ F = m\,a \]

Force equals mass multiplied by acceleration.

Variable Definitions

\(F\) Force (newton, N)
\(m\) Mass (kilogram, kg)
\(a\) Acceleration (m s\(^{-2}\))

Applications

Kicking a Football

A stronger kick (greater \(F\)) gives the ball a bigger acceleration.

Pushing a Heavy Cart

The same push on more mass (\(m\)) produces less acceleration.

Force vs Acceleration

Mass fixed at 2 kg

https://asset.sparkl.ac/pb/sparkl-vector-images/img_ncert/BBgV6NcWG8UQKjluEWKPe0DRWTT9rSA4pRYfDwhj.png

Straight-line graph for a 2 kg object

Mass fixed at 2 kg

Because \(F = m a\), keeping mass constant makes force grow linearly with acceleration.

Key Points:

  • Graph is a straight line through the origin.
  • Slope equals mass: 2 N per m/s².
  • Double the acceleration → force doubles.

Multiple Choice Question

Question

A 4 kg object accelerates at 2 m/s². What force acts on it?

1
2 N
2
4 N
3
6 N
4
8 N

Hint:

Use the formula \(F = m \times a\).

Key Takeaways

Force changes motion

A net push or pull makes an object speed up, slow down, or turn.

Mass resists change

Heavier objects need more force because their mass offers greater inertia.

Acceleration links both

Acceleration tells how fast motion changes: \(a = \frac{F}{m}\).