This Week's Experiment - #277 Newton's Laws
This week we will investigate Newton's laws of motion. While Galileo laid
the foundations for them, Newton was the one that put them into the form that
we know them today. You will need:
a bathroom scale
an object that weighs at least a few pounds
Start by placing the scales on a flat, hard floor. Step onto the scale and
look at your weight. Aaarrrrrggghhhh! OK, so I have done a few too many
experiments involving cookies and ice cream. Now pick up the object you
selected. Notice the new reading on the scales. It should be a bit higher
for the total of you and the object. So far, everything is just as you would
expect.
Now we will change things a bit. As you watch the reading on the scale,
quickly lift the weight up over your head. Do this as quickly as you can.
Did the reading on the scale change? Yes, it should have gone several pounds
higher and then quickly back down. Next, bring the weight back down as fast
as you can, again watching the scale. This time, the reading goes down by
several pounds and then pops back up.
Why does this happen? We can explain it all with Newton's three laws of
motion. They are:
1. A force is required to set an object in motion. It will continue to move
in a straight line in a constant velocity unless another force acts on it.
Newton's first law is often called the law of inertia. Inertia is the
tendency of an object to stay at its state of rest or motion.
2. The acceleration of an object is directly proportional to the net force
acting on it and is inversely proportional to its mass. The direction of the
acceleration is in the direction of the applied net force.
3. For every action (or force) there is a reaction (or opposing force) of
equal but opposite direction.
They may sound complex, but it is really not that difficult to understand
them once we start applying them to our experiment.
When we start, neither you nor the weight you are holding is moving on the
scale. Newton's first law of motion tells that it will require some force to
make a change in the objects movement. It takes force to start it moving.
It takes force to stop it from moving. You are providing the force when you
move your arm up or down.
Newton's second law tells us that the more mass the object has, the more
force it takes to make it move or change its motion once it is moving. The
heavier your object is, the more the reading on the scale will change.
Notice I said mass, not weight. Here on Earth, weight and mass mean pretty
much the same thing, but while weight changes with gravity, an object's mass
remains the same.
Newton's third law tells us that when you push upwards on the object, you are
pushed downwards with the same amount of force. That downwards force on your
body is what changes the reading on the scale. When you pull downwards on
the object, you are pulled upwards, again with the same amount of force.
Again, this changes the reading on the scale.
These three simple laws describe the motion of everything from a baseball to
the space shuttle. Too bad they won't negate the impact of all that ice
cream.
From Robert Krampf's Science Education Company
PO Box 60982
Jacksonville, FL 32236-0982
904-388-6381
krampf@aol.com
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