Question

I need a detailed explanation!

In terms of Newton's Second Law, F = ma, why does it hurt when you kick a brick wall, but not when you kick a soccer ball?



Your task: Write a paragraph explaining why you would experience a different sensation when kicking a brick wall and a soccer ball.

Answer 1

Its simple if we check second law of Newton

`\\ \rm\Rrightarrow F=ma`

`\\ \rm\Rrightarrow F\propto m`

• If mass is more force is more and vice versa

Wall has bigger mass so for force is required and hence more reaction force(Newton's third law)

Answer 2

The brick wall has less mass compared to the soccer ball. With the ball you would have to use less force to make it go a certain distance. You would have to apply more force in the case of the brick wall to get it to go the same distance as the soccer ball.

Heavier things need more force and acceleration to move the same distance as lighter things because they have more mass.

Force by wall.

Take mass of wall as 120 kg and acceleration as 10m/s^2, Then the total force acting would be F = ma

120 * 10 = 1200 N

According to Newton's 3rd law of motion, Every action has an equal and opposite reaction. So, the force you apply on the wall is equivalent to the force the wall applies on you. Hence the wall applies a force of 1200 N on you which is why you get hurt.

Force by soccer ball.

The mass of a soccer ball is obviously lesser than the mass of a wall. Take mass of soccer ball as 0.5 kg and take the same acceleration as 10m/s.

F = ma, Hence

Force = 0.5 * 10 = 5 N

The force applied on the ball is much less compared to the force applied on the soccer wall that is just 5 N. Using the 3rd law of motion, we can prove that only a force of 5 N acts on us when we kick a ball. Hence it does not hurt.

Thus, proved.

Hope this helps.