If you think this carton of milk is big, you should see the cow that produced the milk!

Milk carton water wheel

Ever held a toy under your running bath water? Did it spin or twist away from you? This is explained by a law proposed by a guy named Sir Isaac Newton. Specifically the law states that ‘for every action there is a equal and opposite reaction’. You know, kind of like when you smack your big brother you know you’re going to get smacked back. OK, so maybe that’s not such a great example. Here’s one that will aptly demonstrate Newton’s law.

  1. Poke a hole in the bottom left hand corner of each of the four faces of a half-gallon, paper milk carton.
  2. Now poke a hole in the top flap of the milk carton. Tie a string through this hole.
  3. While covering the holes in the milk carton, pour water into the carton (unless you have more than 2 hands, you may need some assistance with this step).
  4. Suspend the carton in the air by holding on to the string only.
  5. Now take your fingers off of the holes (did we mention that this should be done outside or over a sink – oh well, too late now).

Newton’s Third Law states that every action has an equal and opposite reaction. Water shoots out the holes, and pushes back on the carton with equal force. A turbine is formed as the energy of the moving liquid is converted into rotational energy.

Parent/Teacher/Advanced Notes

In the 1600’s, the English scientist and mathematician Sir Isaac Newton proposed three laws of motion. Newton’s laws concern the ideal motion of objects and do not take into account air resistance or other friction. However, these laws have enabled scientists to describe a wide variety of motions.

The third law of motion states that for each action there is an equal and opposite reaction. For example, when hot gases escape from a rocket engine during take-off, the rocket is propelled upward. The downward motion of the gases from the rocket generates a reaction of the rocket upward. This reaction helps the rocket overcome air resistance and fly into space. There are many other examples of Newton’s third law. When a rifle fires a bullet, the firing of the bullet is the action and the recoil of the rifle is the reaction. Both are caused by the expanding gas of the exploding gunpowder. Rotating lawn sprinklers propel a spray of water in one direction while rotating in the other direction.

Sometimes the reaction is such that it cannot be easily seen. When you throw a ball against a wall and the ball bounces back, you do not see the wall moving in the opposite direction. But there is a small motion of the area of the wall that was hit. If the ball bounces from the ground, the earth also draws back, but the mass of the earth is so great that we cannot see its motion.

Experiment Supplies

Supplies: String, Milk carton


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