# Physics Applications

December 30, 2014

Here are a few examples of physics you observe in your everyday life.

1. Balancing a see-saw:

If you have two people with different weights it is impossible to maintain the board balanced if they are both sited the same distance from the axis of rotation since for a system to be balanced there needs to be equal torques. To make the board balanced with different weights you need to increase the lever arm (lever arm = smallest distance from the axis of rotation, always perpendicular to force) of the person with the least weight so that the torques equal. In practice the heaviest person of a see-saw needs to sit close to the center while the lightest one sits away from it.

2. How a credit card works?

A credit card works because it contains magnets placed in a specific pattern. The credit card machine has coil of wires that cause a change in magnetic field when the card is swiped. This process is called electromagnetic induction. The change in magnetic field induces a voltage that creates a current that is used to signal your account information to the machine.

3. How do you walk?

Newton's third law states that every action has an equal and opposite reaction. This is relevant to walking because when you put your foot on the ground, you are applying a force to it. In doing this, the ground also actually applies an equal force onto your foot, in the opposite direction, pushing you forward.

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