Fun Classroom Demonstrations for Newton's Laws
How to Liven up Science Lessons by Demonstrating Physical Principles
Dec 20, 2008
Newton's laws are often taught by having students memorize the words for the laws without understanding the concepts. There is no better way to make students hate physics and science in general. Physics is exciting; physics lessons should be equally exciting.
One excellent way to excite students about learning physics, or other sciences, is using classroom lecture demonstrations. Ideally demonstrations clearly illustrate the principle and are dramatic enough to excite students about learning physics.
There are many good ways to demonstrate Newton's laws. This article gives a few that will keep students interested in the lesson. They are easy and cheap to use. Teachers should try out demonstrations before class to make sure they work.
Pedagogically it is good to ask students to think about what will happen before showing them and to do the demonstration before explaining the concept.
Equipment Needed
- Empty aluminum drink cans,
- Hammer,
- Lead or iron weight about the size of a brick,
- Toy water rocket or other rocket.
Newton's First Law
Rest the weight on the can. Strike the weight with the hammer as hard as possible without crushing the can. Remove the weight and strike the can directly with the same force, crushing the can. The weight at rest wants to stay at rest, so the blow does not move it downward to crush the can. Show that a similar sideways blow to the weight does not significantly accelerate it. It is also possible to place one's hand under the weight and strike the weight without hurting one's hand.
Students may suggest that the can is not crushed because the weight distributes the blow of the hammer over a larger area. They are correct. There is more than one principle protecting the can, so it is possible to add a lesson on pressure to the lesson on Newton's laws.
To demonstrate that an object in motion wants to keep moving, simply drop the weight onto the can. It will continue to move, crushing the can, until the table provides a stopping force. Trying this with someone's hand is a bad idea!
Newton's Second Law
Using the same amount of force, strike both the weight and the can sideways with the hammer. The less massive can accelerates much more. Compare a gentle tap on the can, or weight, with a hard blow. Larger forces produce larger accelerations.
Discuss the force required to slide a very massive object, such as a refrigerator. Now introduce Newton's second law: Force = Mass X Acceleration.
Newton's Third Law
Newton's third law governs rocket propulsion, so firing a rocket is an excellent way to demonstrate this law.
Small solid fueled hobby rockets can soar to hundreds of feet. They provide a memorable demonstration, however teachers using them for a class must take great care to enforce safety rules.
Small plastic water rockets provide a simple safe alternative. Toy plastic water rockets are not as easily available in toy stores as they were a generation ago, however internet suppliers can be found. Students are often entertained if the teacher gets a little wet launching the rocket.
Blowing up a balloon and letting go provides an even simpler alternative.
According to Newton's third law, the rocket pushes the water (or other fuel) backwards, so the water pushes the rocket forward with an equal and opposite reaction force. Tell more advanced students the law of conservation of momentum also governs rocket propulsion.
These classroom demonstrations can illustrate Newton's laws and can be used for any age group from elementary school kids through college students.
 |
