The Frozen Lake

You wake up on a frozen lake in an isolated region. The surface of the lake is frictionless and no grip of any kind can be attained over it. You find just your mobile phone in your pocket, but when you take it out to call for help, you realize there is no reception.

If there is no wind force to help you escape, what are you going to do to avoid freezing to death?

Throw your phone as hard as you can. Thanks to Newton’s third law of motion and the frictionless lake, you will start sliding away.

Balloon in a Car

You are sitting in a motionless car, which is tightly sealed, i.e. no open windows, holes in the car, etc. A helium balloon on a string is tied to the floor. If you start accelerating the car, is the balloon going to move back, forward, or stay in place?

The reason the balloon floats up in the air is that the helium has a lower density, so when gravity pulls the denser air around down, the balloon gets pushed up. Similarly, when the car accelerates, the air around gets drawn to the back of the car, which makes the helium balloon go forward.

The Golden Cylinder

You are shown two cylinders – one of them is made of gold and hollow, the other one is made of alloy and solid. Both of them have the same weight, shape, and are colored in black. How can you figure out which cylinder is the golden one, without scratching the paint?

Simply roll the two cylinders on the ground. The hollow one will roll farther than the solid one since it will have a higher moment of inertia.