As you are reading this, you are probably aware of the chair (or the floor) pushing your body up, but you might not be aware that your body is actually moving.  As the earth spins and rotates around the sun, all of the bodies on it are in motion.  We just don’t realize it because we are part of the system that is moving.   It’s like when you’re in a car that is moving, unless you’re watching out the window you can do other things, like read or play video games or watch a movie.  

Suppose you’re doing your homework while riding in a car and the driver slams on the breaks, what happens to your motion within the car?  It might feel like you get jolted forward, you may even mess up your homework or spill your drink.  How objects move became a topic of interest for a scientist named Isaac Newton, around 1665.   A familiar image of Newton is one where he is sitting under an apple tree and an apple falls on his head, an event that supposedly inspired Newton’s studies of motion and mechanics.  From his studies of how objects move, Newton developed three ideas that were verified by other scientists over the years and were eventually established as scientific laws.  Recall that a law is something in science that describes what will happen. 

Newton’s First Law
The first law says that an object at rest tends to stay at rest, and an object in motion tends to stay in motion, with the same direction and speed.  Motion (or lack of motion) cannot change without an unbalanced force. If nothing is happening to you, and nothing does happen, you will never go anywhere. If you're going in a specific direction, unless something happens to you, you will always go in that direction.  Newton’s First Law of Motion is also called the Law of Inertia. 
What if you threw a ball as hard as you could?  Newton’s Law of Motion would predict that the ball would continue to move forever, but you know that isn’t the case.  The ball will eventually come to a stop.   You must then conclude that some other forces were acting on the ball.  In this case, air resistance, gravity, and friction are forces that act on the ball and cause it to eventually come to a stop.   However, in places without these opposing forces, like outer space, the ball would just keep moving.  

Newton’s Second Law
Now imagine also two sumo wrestlers, one weighs 250 lbs  (113 kg)  and the other weighs 50 lbs (23 kg).  Which one is going to be easier to move?    Objects that have more weight will require a greater unbalanced force to move. In this case, the heavier wrestler has an advantage over the lighter one.   In sports, wrestling has heavyweight and lightweight categories to keep the competition fair.

Newton’s second law states that the acceleration of an object produced by its total applied forces relate to the object’s mass. The greater the mass, the greater the force needed to accelerate (or move) the object.   Accelerations can be both positive and negative.  It can require a lot of combined forces to push large truck (many people).    Also a large truck will require much more force to stop once it gets going.  Newton’s second law also gives us an exact formula for determining how much force is needed to accelerate an object.  Force = mass x acceleration.

Newton’s Third Law
The third law says that for every action (force) there is an equal and opposite reaction (force). Forces are found in pairs.   For instance, the force of your body is pushing down on the chair you are sitting on while the chair is pushing you up.  Imagine what happens when you step off a boat and onto a dock.  When you step away from the boat, you actually push the boat in the opposite direction.   Here’s another example.  You and your friend are ice skating and you stop to face each other.  Your friend reaches out and shoves you.  You slide backwards on the ice, but what happens to your friend?   He moves in the opposite direction.   For every action, there is an opposite reaction.

Name _________________________________________Date _______

QUESTIONS:  (circle the correct answer)

1.  In science, what is a Law?
a.  a rule about nature that describe how things work
b.  standards of behavior that people choose to abide by
c.  an educated guess about what may happen in the future

2.  In a wrestling match it is discovered that the athlete lied about his weight to gain an advantage over his opponent.   Based on what you know about inertia, how did the cheater lie?
a.   he claimed he weighed less than he actually did
b.   he claimed he weighed more than he actually did

3.   Which law gives us a formula for determining how much force is required to move an object?
a.  first law           b.  second law               c.  third law

4.  You roll a ball down a hill.  The ball rolls for a distance and eventually comes to a stop.  What stops the ball?
a. inertia              b.  acceleration              c.  air resistance        

5.  For every action, there is an opposite reaction.  This statement describes:
a. Newton’s first law        b. Newton’s second law       c.  Newton’s third law   

6.  Two objects are sitting at the top of a building.  One object weighs 16kg and the other weighs 45 kg.  Which will be easier to push off the edge of the building?      a.  16 kg  object        b.  45 kg object       c. both are equal

7.  You are in a canoe on a lake and another canoe floats next to you.  You use your paddle to push the other canoe away so you don’t bump. As the second canoe is pushed left, what happens to your own canoe?
a.  it stays stationary              b.  it moves right               c. it moves left also

8.  The motion of the two canoes in #7, is described by Newton’s __ Law.
a.  first               b.  second           c.  third