Physics for Kids: Newton’s Three Laws

Sir Isaac Newton is famous for his three laws of motion.  Although these laws are often not taught until high school in many science classes, the fact is that there are many activities that highlight these laws and can be taught to children as young as preschool.  In fact, like any topic, the more exposure a child has to it, the better the knowledge is cemented and the greater the understanding.  With this in mind, it is worthwhile to consider introducing activities and concepts that centre on these laws of motion so that by the time your child hits high school science, this is nothing but a breeze…

Newton’s First Law of Motion: Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it.

What does this mean?  It means things will keep doing what they’re doing unless acted on in a way to change that.  Roll a ball and it would keep rolling without other forces acting on it.  This is a great way to introduce the concept of invisible forces like gravity and friction.

Activity:  Get your child (or children) together with a ball that can be rolled a fair distance.  In the first case, start rolling the ball, but have the child stop it by grabbing it part way.  Explain that the child grabbing it is the external force that keeps the ball from continuing to move.  In the next example, have the child roll the ball gently enough that it won’t run into anything but will stop on its own.  The ball stops – why?  Did the child see any force stop the ball?  No and that’s because the force that acted on it was friction – an invisible force.  You can do the same thing by throwing a ball up in the air.  It doesn’t continue, but why?  Gravity, another invisible force.  You can now go on and work on other experiments that help clarify the roles of these forces in our universe.

Newton’s Second Law of Motion: The relationship between an object’s mass m, its acceleration a, and the applied force F is F = ma.

This is a long way of saying that the change in acceleration that happens to an object is dependent upon its mass and the force applied to it.  There’s a lot to learn from this, and children are actively learning this one on a day-to-day basis, so the main point for you as parent/teacher is to simply point it out to them.

Activity 1:  Take the same ball and have it start at rest by the child.  Ask the child to push it gently and see how long it takes for the ball to reach a set point (e.g., the other side of the room).  Now bring the ball back and ask the child to push as hard as s/he can and measure the time again.  The second push should make the ball go faster because there was more force exerted on it and the mass remained the same.  This highlights to children how they can use force to change the acceleration or motion of the object.  Have them brainstorm ways they use this is sports (e.g., think of hockey and the different type of shots there are).

Activity 2:  Get two balls of very different weights.  Have a child push the lighter ball with moderate force and measure how long it takes to get to a set point.  Now have the child push the heavier ball with the same force (as much as possible) and measure how long that ball takes to get to the same set point.  You can point out to the child that the times are different but the force was nearly the same… why?  This is the effect of mass on motion in that heavier objects require more force to reach the same acceleration as an object with less mass.  Again, have the children think of times when they have seen this in their lives.

Newton’s Third Law of Motion: For every action there is an equal and opposite reaction.

This is my personal favourite of the three laws because not only does it apply to motion, but arguably life as well.  However, in terms of motion, this law keeps the universe (and our things) intact.  This one is also one of the hardest to understand because it involves so many different forces at work.

Activity:  Using two balls of the same weight, send one ball crashing into the other.  What happens?  The children should see the ball that was at rest go flying away, but what about the other ball?  It likely either stopped or even went backwards a bit.  The reason for this is Newton’s Third Law of Motion: The ball that was at rest exerted a force onto the moving ball, the exact same force that hit it.  This force acted on the motion (see Law 1) to stop or even reverse it.  What if the two balls had different masses?  What would happen then?  You can either talk about it or have them work it out themselves using the balls that were part of the activities for Newton’s Second Law of Motion.

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Introducing physics at a young age is not only doable, but is fun for kids and helps them integrate and consolidate their knowledge before they have to truly understand it in the high school years.  Will they fully understand these laws right away?  No, but that’s okay.  With repeated exposure and ongoing activities and discussion, the knowledge becomes cemented in ways that don’t happen when it’s rushed through later on.

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