Physics Activities
for Middle School
Middle school is a time to build students' physical intuition, before they can learn physics through algebraic equations and calculus. Newton's car, liquid barometers, and lasers pointed through jars of water help introduce students to forces and light properties in ways that may surprise them. .
Newton's Car
One such activity is called Newton's car, which is a demonstration of Newton's third law of motion. The third law dictates that for each action, there is an equal and opposite reaction. This means that, if you push on something, it will push back on you just as hard. The Newton car demonstrates this by ejecting a weight off the back to propel itself forward with a released rubber band. Though the car pushes the weight, the weight also pushes the car with equal force. Another way of looking at it is a demonstration of Newton's first law, the law of inertia. Because of the weight's inertia, the car is able to push off it, just as it might push off a wall. NASA provides instructions for build a Newton's car.
Calculate Buoyancy and Density
The volume of water displaced by a submerged object is pushed up with a buoyant force equal to the weight of the displaced water. This is Archimedes' Principle. So hanging an object from a scale while it is above water and below water tells you how much water the object displaces, and therefore what the volume of the object is. The density of the object is therefore found from its weight and volume.
The discussion of Archimedes' Principle can be extended to the difference between icebergs and glaciers. Icebergs don't raise sea levels as they melt, because they already displace a volume of water of equal mass.
Measure the Small
Small objects can be too small to detect with available instruments. A simple measurement idea, to show that physical laws hold at small scales, is to measure the aggregate effect of many, many small objects. Then the total effect, divided by the number of such objects, gives you the effect of just one.
The activity can be as simple as counting out a few bags worth of jelly beans or few pounds of lead shot, weighing the bunch, then dividing by the count to get one unit's weight.
Discussion with students will be instrumental to put this activity in context; otherwise, it might come off as busy work. This activity prevents students' struggling in high school physics class with the idea that scientists know the effect of the small, even if it is not directly measurable. A simple example is that, despite being small, a fly hitting a car's windshield slows the car down, due to the conservation of momentum. Another example is that the moon has little effect on a drop of ocean water, but can cause mile-deep ocean water to bulge by a few inches, creating a tide when the bulge comes in to shore, as first explained by Newton.
Electrical Induction
Connect a wire to the two poles of an ammeter or of a light bulb. Then wave a magnet back and forth over the wire. The light or ammeter will flicker because the wire is cutting the field lines of the magnet. Danish scientist Hans Christian Oersted discovered this effect in 1819 while giving a lecture. For a stronger effect, coil up the wire and use a larger magnet. This effect is the basis of the alternating current power grid and much of modern electronics.
Tags: Activities Middle, Activities Middle School, Archimedes Principle, demonstration Newton, example that, ocean water, Physics Activities
