Classical Mechanics

Introduction to Forces

Introduction to Forces Warmup


When a bus that's moving forward applies its brakes, the passengers feel a jerk. In which direction do they feel the jerk?

Paul throws a book onto flat, frictionless ground. He notices that there are two forces acting on it: one is the gravitational pull from the Earth and the other is the normal force from the ground.

How will the book move once it hits the ground?


  • Neglect the drag due to air.

Why does a seasoned cricket player draw his hands backwards while catching a ball?

When a block is hung on a spring balance, then its reading is A.
When a beaker with water in it is placed on a weighing machine, the reading is B.
Now, the block is immersed in water as shown.

What will happen to the readings of the spring balance and weighing machine?

Newton's third law states that forces occur in pairs

"For every action there is an equal and opposite reaction".

Suppose a block is placed on a table. The block pushes on the table in the downward direction, and in return, the table pushes the block in the upward direction.

What can we say about the magnitude of these forces?


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