Forces surround us constantly. We need force to play sports, to open a bottle and even to write!
Lets discuss the mechanics of the world around us in this last chapter of the year.

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Discussion in class:
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If you are riding a bus and suddenly, the bus comes to a stop. What do you feel?
If you take the elevator, how do you feel if you go up? Or down?
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In a game of “tug-o-war”
Now think about your favorite sport. What kind of forces does it entail?
There is also a push or a pull.

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The symbol of force is “F” and the unit of measurement is “newton” or “N” ex: 5 N ou 20 N
A force is a mechanical action that sets an object in motion.
 A force can change the speed and trajectory of an object already in motion.
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 It can also deform an object.
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Ex: - Throw a baseball
Skating
Push (or pull) a drawer
Compress a sponge
Etc.

We will discuss a few different types.
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Compression: it is a force applied to compress an object. It can provoque or modify and object’s motion.
Ex: compressing a balloon!
Also, the muscles in your arm must compress to lift objects.
Torsion: the action of compressing in rotation direction

 Tension: the force applied to pull an object in one direction.
(especially on a rope)
Ex: Such as in the game of tug-o-war or like the acrobats.
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Flexion: When an object is pulled and pushed at the same time.
Shearing: When you pull on opposite direction to tear something
 Friction: It is a force that slows down or stops the movement or motion) between two surfaces.
Friction acts in the opposite direction of the motion.
Ex: Your shoes have rubber, so you dont stop and fall.
Also the tires from a car.
Air resistance is also a source of fricftion.

What is the purpose of a zamboni?
To reduce friction between the skates and the ice.

What is the difference between these vehicles?

All have a slender body, which makes for less air friction http://www.youtube.com/watch?feature=pla yer_detailpage&v=KIeXEiJuJUY

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Elastic deformation: ex trampoline (takes its original shape).
Permanent deformation: ex:can of soft drinks that changes shape (it will take any shape, different from the initial shape)
Rupture: material breaks like the cables of the
Olympic stadium.

WHAT DO
THESE 3
SYSTEMS
HAVE IN
COMMON?

WHAT DO THESE 4
SYSTEMS HAVE IN
COMMON?

WHAT DO THESE 3 SYSTEMS HAVE IN COMMON?

 Definition:
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The translational movement is the movement that an object or part of an object does in a straight line.

 Definition:
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It is the type of movement that a piece of an object or the entire object will do around an axis.
 Sometimes the rotation is partial:
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Part of the object is immobile, while the other part rotates.
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Ex: a door handle

 Sometimes in some objects rotation and translation are combined. Thus creating a movement that looks like a spiral.

Newton , is a british physist, born the year
Galileo died. He attended Trinity College at
University of Cambridge in 1661, he did his own research and taught while he was still a student!
His work " Philosophiae naturalis principia mathematica ", was published in
1687, has three sections and contains the universal law of gravity and the famous
Newton’s laws of motion.

 The first law, also known as inertia, states that all objects tends to remain in the same speed and direction it was moving at (even at rest) unless an outiside force acts upon it.
In a roller coaster, the train keeps moving until the breaks are applied.

The golf ball remains at rest until an outside force acts upon it.

All acceleration of an object is proportional with the forces applied on it. All acceleration is inversely proportional to the mass.
Examples of acceleration:
Example 1: The more we pull on a rope at tug-o-war, the more we accelerate.
Example 2: A person pushing a table, is not the same as three pushing a table. The three together will accelerate way more!
Examples with mass:
If these same three people applied the same force on a car, they won’t accelerate as much. Because it’s a lot heavier.

To every action, there is an equal and opposite reaction

The second and third laws applied on roller coasters…
2 nd law
The force that we feel from the gravity as we free fall from a very big height is enormous and can be calculated:
Using F = mxa m = mass of the train and passengers.
a = gravitational acceleration (g)
9.8 m/s 2
3d law
The roller coaster undergoes curves that you can feel. When the train goes in a curve we feel like the seats are pushing us.
But you are also pushing the seats with an equal and opposite force. Which helps you to hold on to your seat!