• Balloons can be used to explore the properties of gases.balloons 1 image by Pix by Marti from Fotolia.com
  
  Although physics can be very challenging to teach, it can also be very rewarding. There are a number of exercises that can help instructors illustrate key physics concepts while engaging the students in interesting and fun experiments that will leave them loving physics and loving class.
  
  

Growing Balloons

• The University of Virginia physics department suggests "growing balloons" for students to explore such physics concepts as states of matter, heat absorption, heat transfer and kinetic motion. The exercise is relatively simple and requires only two balloons, a heat source and a cooling source like cold water or a refrigerator, and the instructor may choose to demonstrate the activity or allow the students to experiment themselves.
  
  The balloons should be inflated to about ¾ of their maximum capacity. Students then measure and record the diameter of the balloons. One of the two balloons should then be warmed by holding it near a heat source like a lamp. The students will see the balloon expand as the air temperature in the balloon rises. They should then measure and record the diameter of the balloon again for comparison and a discussion should follow on how gases expand in heat. Next, take the second balloon and submerge it in cold water. Students should witness the balloon shrinking as the air temperature within the balloon decreases. A final measurement should be taken and recorded and a further discussion of gases contracting in cold should follow.
  
  

Parachute Games

• Leticia Rodriguez and Ferdinand Peck from the Illinois Institute of Technology recommend exploring gravity and its relationship to mass by designing a simple parachute out of newspaper and attaching a varying number of paperclips to the chute. The parachute itself is simply a 22 inch by 22 inch square of newspaper with four lengths of 4 inch string, each string attached to a corner of the newspaper and the four strands knotted together. Students should then tie one paperclip to the parachute, drop it from a designated height, and measure and record the amount of time it takes for the paperclip to reach the ground. Students should then repeat the experiment adding more and more paperclips, each time dropping the parachute from the same distance and measuring the amount of time it takes for the paperclips to land. A discussion should then follow about the relationship between mass and gravity. (Teachers might also perform the same experiment dropping the parachute from varying heights and explore the relation between height and gravity as well.)
  
  

Magic Acts

• Peter Insley from the Illinois Institute of Technology suggests teaching inertia by way of a classic magic trick: pulling a tablecloth free off a table without disturbing the dishes. The dishes on the tablecloth should be heavy and the glasses full of water. For those instructors who would rather not risk broken dishes and spilled water, Insley offers a less risky exercise in inertia that requires a stack of nickels and a credit or library card. The student should attempt to flick the bottom nickel out from beneath the stack with the card. He should notice that the larger the stack of nickels, the easier it is for him to flick one free. After completing the experiment a discussion on the relationship between inertia and mass should follow.