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Newton’s Laws of Motion. 1. The Law of Inertia 2. F=ma 3. Action & Reaction. Newton’s Laws of Motion. 1 st Law – An object at rest will stay at rest, and an object in motion will stay in motion at a constant velocity, unless acted upon by an another force. - PowerPoint PPT Presentation
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NEWTON’S LAWS OF MOTION
1. The Law of Inertia2. F=ma3. Action & Reaction
Newton’s Laws of MotionNewton’s Laws of Motion
11stst Law Law – An object at rest will stay at rest, and an object in motion will stay in motion at a constant velocity, unless acted upon by an another force.
22ndnd Law Law – Force equals mass times acceleration.
33rdrd Law Law – For every action there is an equal and opposite reaction.
11stst Law of Motion Law of Motion The Law of InertiaThe Law of Inertia
An object at rest will stay at rest, and an object in motion will stay in motion at constant velocity, unless acted upon by an unbalanced force.
Inertia is the tendency of an object to resist changes in its velocity.
1st Law- Inertia
These basketballs will not move unless acted on by a force.
1st Law Once a force
actied on it -motion-it would never stop!!
~ unless acted on by a force (push, pull, gravity, air or friction)
1st Law
Unless acted upon by an unbalanced force, this golf ball would sit on the tee forever.
…BUT…
F
R
I
C
T
I
O
N
Why do we observe every day objects in motion, slowing down and eventually stopping without an outside force acting on them?
It’s a force we sometimes cannot see…
ALL objects on earth are under the influence of friction.
Unlike the frictionless space the moon travels through.
Let’s review friction…
The force that two surfaces exert on each other when they rub against each other.
It depends on…
Static Friction Sliding Friction Rolling Friction Fluid Friction
Friction is… The 4 types of friction:
1. How hard the surfaces push
2. The types of surfaces
Slide your book across your desk gently and watch it come to a stop. WHY? The book comes to a
rest because a force was exerted on it - friction - which brings the book to a rest.
According to Newton’s 1st law, the book would continue in motion at the same speed
and direction - forever! (Or at least to the end of the desk.)
if it wasn’t for that unbalanced force acting on it-
FRICTION!!!
Newtons’s 1st Law and You
Because of inertia, objects (including you) resist changes in their motion. When the car going 80 km/hour is stopped by the brick wall, your body keeps moving at 80 m/hour.
Don’t let this be you!
Wear seat belts.
Mass Matters!!!
The greater the mass an object has, the more force it will take to put the object in motion- therefore it will have a greater inertia
Newton’s second law says that the amount of acceleration needed to make an object change its motion depends on the MASS of the object and the net force required. SOOO…if you want to find force:
Force= mass x acceleration The 2nd Law
2nd Law Lets try it out!
How much force is needed to accelerate a 1400 kilogram car 2 m/s2?
Write the formula
F= M x A
Fill in the formula. (Don’t forget units!!!)
F= 1400kg x 2m/s/s
Solve the formula.
2800 N
Newton’s 2nd Law proves that different masses accelerate to the earth at the same rate, but with different forces.
• We know that objects with different masses accelerate to the ground at the same rate.
• However, because of the 2nd Law we know that they don’t hit the ground with the same force.
F = maF = ma
98 N = 10 kg x 9.8 m/s/s98 N = 10 kg x 9.8 m/s/s
F = maF = ma
9.8 N = 1 kg x 9.8 9.8 N = 1 kg x 9.8 m/s/sm/s/s
For every action there is an equal and opposite reaction.
Newton’s 3rd Law
3rd Law
According to Newton, whenever two objects interact with each other, they exert forces on each other. When you sit in your chair, your body exerts a downward force on the chair and the chair exerts an upward force on your body.
Its BALANCED!!
3rd Law
There are two forces resulting from this interaction - a force on the chair and a force on your body. These two forces are called action and reaction forces.
Newton’s 3rd Law in Nature Think about a fish
swimming through water. A fish uses its fins to push water backwards. In turn, the water reacts by pushing the fish forward, moving the fish through the water.
The size of the force on the water equals the size of the force on the fish; the direction of the force on the water (backwards) is opposite the direction of the force on the fish (forwards).
Other examples of Newton’s Third Law The baseball forces
the bat to the left (an action); the bat forces the ball to the right (the reaction).
3rd Law
Think about your car or bus ride on the way to school. Both are equipped with wheels which spin backwards. As the wheels spin backwards, they grip the road and push the road backwards.
Momentum
…IT’S THE PRODUCT OF MASS AND VELOCITY
Momentum = mass × VELOCITY
The unit is….
Kg × m/s WITH A
DIRECTON
If a small object is traveling at a high speed it can have more momentum that a more massive
object traveling at a lower speed.
MASS MATTERS!!
The Law of Conservation of Momentum
In the absence of outside forces, the total momentum of objects that interact DOES NOT CHANGE
What outside forces?!? Gravity and FRICTION!!!
Movements in Momentum
The total momentum of any group of object remains the same, or is conserved, unless an outside force acts on the objects.
FRICTION!!!
It is a type of conservation of momentum.
Momentum can be transferred from one object to another
Conserving Momentum Transferring Momentum
Collision with 2 moving objects
4m/s
2m/s
2m/s4m/s
Collisions with 1 moving object
4m/s
0m/s
When the blue car hits the yellow car, it will transfer its momentum to that car. The yellow car would move at 4m/s and the blue car would be at rest.