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Unit 2: Motion Page 12
will hit a lot harder than a opposite direction. As you sit on
bumblebee colliding at 30 mph. your chair reading this, gravity is
pulling down with a certain force
The more mass something has, the (the force of your weight and the
more force that’s needed to get it weight of the chair). The floor is
to accelerate. a=F/m This, by the pushing up with the same force.
way, is a mathematical definition
for acceleration. For example, it is Quick quiz - what would happen if
a lot harder to get a train to the floor pushed up with more
accelerate than it is to get a ping force than force of the chair
pong ball to accelerate. pushing down? There would be an
upward force which would cause an
Now here’s an interesting acceleration of the chair causing
definition. The definition of mass your mass to lift upwards! (That’s
can be stated as m=F/a. In other Newton’s Second Law, right?)
words mass is how much force it Because the force up and the force
takes to accelerate something. This down is equal, the net force is zero
is a major difference between mass and there is no motion.
and weight. Something with great
weight on Earth may be weightless This law helps you walk. As you
in space (since there’s no gravity) walk, you push backwards against
but it will still be just as difficult to the ground. The ground gives an
get it to accelerate. equal and opposite push to you so
you move forward. Try to imagine
Newton's Third Law someone walking in a canoe. (I
don’t recommend trying this,
Are you ready for Newton’s Third unless you know how to swim and
and final law of motion? Every are willing to get wet!) As the
action has an equal and person steps forward, the canoe
opposite reaction. Even though moves backward. The equal and
this is the most well known of opposite force of the walking
Newton’s Three, it seems to me to moves the person forward just as
be the hardest to fully far as it moves the canoe
comprehend. backward.
Again, it is a tribute to Newton that “But how come as I walk on my
he was able to “see” this law. For floor, my house doesn’t move
every action, every force, the same backwards like the canoe?” Ahhh,
action/force happens in the good, I’m glad you’re paying
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