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# PHY100H1 Chapter Notes -Elastic Collision, Net Force, Inelastic Collision

Department
Physics
Course Code
PHY100H1
Professor
Vatche Deyirmenjian

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Classical Mechanics!
So, what is Motion?
Everything in the universe moves.
1.Motion is one part of what physicists call as Mechanics. The physics
of motion is all about forces!
2.Forces need to act upon an object to get it moving, or to change its
direction
3.Because, changes in motion do not just happen on its own! So we
need forces to get things happen!
4.Physicists uses standard deviations of second(s), meter (m), and
kilogram (kg) when they study motions of an object
Velocity and Speed? Are they the same thing?
No! Velocity is a vector, whereas speed is not.
Vector is a numerical value in a specific direction, and used to describe a
specific amount of force and its direction! The amount of force is what we
call as magnitude.
Velocity!
1.Therefore, velocity is the speed of an object and the direction it is
moving.
2.Velocity is also the rate of motion in specific direction
3.Velocity can be constant or it can change by acceleration (forces)
Speed!
1.Speed, can be calculated by the formula of:
(Change in position/distance)/ (change in time)
2.Speed with a direction is velocity
Thought Experiment:
If I tell you I'm driving north and ask you how long until we get to the city.
You can't know the answer since you don't know my speed. You need both
values.
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Okay, what about Acceleration?
Acceleration is a way to measure how fast something is speeding up.
Decelerating is when something is slowing down.
Both of these phenomenon happens when we are trying to change the
velocity
1.Acceleration is also a measure of how much the velocity of an object
changes in a certain time, usually per second.
2.We can calculate acceleration with this formula:
(Change in velocity/change in time)
Thought Experiment:
One important cause of acceleration is gravity. Suppose you dive off a cliff
or a high diving board. You will start off falling slowly, but as gravity pulls
on you, you will speed up (accelerate) until you are going very fast.
But, can acceleration be constant?
Yes!
A great example would be gravity. Gravitys pull of objects is constant here
on Earth, and it always pulls toward the center of the planet.
But this can only work with the absence of air resistance, where all freely
falling objects will accelerate to the Earths surface with the same
constant value for a given location.
Explain what Momentum is!
Momentum is an indicator of how hard it would be to stop an object from
moving.
This is somehow related to Newtons First Law,
isnt it?
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Totally! Newton suggests that any object moving will continue moving
unless it is interfered with. So.
1.The total momentum remains constant at all time, if there is no net
force exerting upon it.
2.A force is push or pull.
3.This is also known as the conservation of momentum.
4.Can be calculated with this formula:
(Mass of an object) x (objects velocity)
Thought Experiment
When you throw a ball at someone and it hits him hard, it hurts because it
was difficult to stop (had momentum). Think about it.
If you throw a small ball and a large ball at the same speeds, the large ball
will hit a person with a greater momentum, be harder to stop, and hurt
more.
When the mass is greater (at the same speeds), the momentum is greater.
Wait, so how to conserve momentum?
It happens in two types of phenomenon namely elastic and inelastic
collision
Elastic collision
1.Happens when a ball hitting the ground, and bounce back off the
ground
2. In this experiment, no kinetic energy is lost
3.All of that energy is still in the object, so we could say that the
energy is conserved
4. If kinetic energy does not change, so does the momentum
5.But the momentum vector does change, because the direction of the
ball changes when it bounce off the ground
Inelastic collision
1.The energy of the ball was not conserved, but the total energy that
was forced onto the ball was conserved
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