Force and Motion Discover why a harder push means a faster move.

Push or Pull

Force

A force is a push or a pull that can change an object's state of motion.

Key Characteristics:

  • Starts or stops motion
  • Speeds up or slows down objects
  • Changes direction of movement

Example:

Name one everyday action that is a push and one that is a pull (e.g., pushing a swing, pulling a drawer).

Pushing a Cart

More Mass, Less Acceleration

A light, empty shopping cart shoots forward with a gentle push.

Load it with heavy bags; the same push only creeps it along.

Greater mass needs a larger force to get the same acceleration.

Key Points:

  • Same push, light cart → quick acceleration.
  • Heavier cart feels harder to push because it accelerates less.

Newton's 2nd Law

\[F = m\,a\]

Acceleration of an object is directly proportional to the net force and inversely proportional to its mass.

Variable Definitions

F Net force (newton)
m Mass (kilogram)
a Acceleration (m/s²)

Applications

Pushing a Cart

More force makes the cart speed up faster.

Kicking a Football

Heavier balls need more force for the same speed.

Worked Example

A 10 N force pushes a 2 kg box on a smooth floor. Find its acceleration using \(F = m a\).

1

Write the formula

Acceleration \(a\) is given by \(a = \frac{F}{m}\).

2

Substitute values

\(a = \frac{10\,\text{N}}{2\,\text{kg}}\)

3

Solve

\(a = 5\ \text{m/s}^2\)

Pro Tip:

Keep units consistent; Newtons for force and kilograms for mass ensure acceleration comes out in m/s².

Quick Check

Question

For a body with constant mass, if the applied force doubles, how does its acceleration change?

1
It halves.
2
It remains unchanged.
3
It doubles.
4
It becomes four times.

Hint:

Remember \(a = \frac{F}{m}\). Keep m constant.

Key Takeaways

Recap the essentials of Newton's Second Law.

Force = Push or Pull

Any interaction that tries to move or stop an object.

Law Connects F, m, a

Acceleration depends on applied force and the object's mass.

Formula \(F = m a\)

Force equals mass multiplied by acceleration.

More Force → More a

With the same mass, larger force gives greater acceleration.

More Mass → Less a

With the same force, heavier objects accelerate less.