How To Catch Coins Falling From Your Elbow

Step 1: You will need

Step 2: Aim

The aim of this experiment is to demonstrate the principle of inertia

Step 3: Method

Stick your elbow out in front of you and place your hand on your shoulder. Balance a stack of coins on top of your elbow. In one rapid motion, move your open hand to where your elbow is and try to catch the coins.
If you move quickly enough, you will be able to catch them in time. If you can't…. Practise!

Step 4: Conclusion

You got it! Great! Give yourself a round of applause, but put the coins down first.
So why did this happen? The coins did not fall to the ground before you caught them because of the principle of inertia, which states that an object that is at rest will stay at rest unless acted upon by an unbalanced force. Gravity is the force which causes things to fall to the ground, but it takes a few moments to kick in. When you moved your arm, the coins' tendency was to remain motionless until gravity acted upon them, making them fall to the ground. When you moved your arm fast enough, the coins stayed still long enough for you to catch them.