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Newton’s Laws of Motion
In this PPT
BLACK text should be recorded in your physics notebook
Purple text does not need to be recorded, or may be on your Notes Supplement worksheet
I will let you know when it is time to refer to your Notes Supplement sheet
Some Vocabulary…
Weight – how strong gravity is pulling on youGravity – a pull towards the center of an object
On Earth, the pull on an object towards the center of the Earth
The more mass an object has, the stronger the pull of gravity.The Earth has a gravitational pull 6 times greater
than that of the moonJupiter has a gravitational pull 2.4 times greater than
that of Earth
Gravity and Weight
Mr. Albano’s weight on Earth is ~60kg.What is his weight on the moon?What is his weight on Jupiter?Does his mass change on the moon? On
Jupiter?
Newton’s First Law of Motion
An object in motion stays in motion unless acted on by an unbalanced force
An object at rest (not moving) will stay at rest unless acted on by an unbalanced force
Newton’s First Law of Motion
Also known as the Law of InertiaInertia – The reason an object stays at rest, or
in motion
Newtons’s 1st Law and You
Don’t let this be you. Wear seat Don’t let this be you. Wear seat belts.belts.
Because of inertia, objects Because of inertia, objects (including you) resist changes in (including you) resist changes in their motion. When the car going their motion. When the car going 80 km/hr is stopped by the brick 80 km/hr is stopped by the brick wall, your body keeps moving at 80 wall, your body keeps moving at 80 km/hr.km/hr.
Newton’s First Law
“Rounding” CornersCan you run around the desk without slowing
down?
“Rounding” Bases
Another Inertia Example
I’m safe over here. That guy is toast!
Stay over there, you’ll
be safe!
Hehehe
More Inertia
“Red Light / Green Light”
“Weightlessness”
Without friction, Newton’s 1st Law is perfectExample – Outer Space
How a shuttle orbitsWeightless = Falling???
GRAVITY
Forward Inertia
Parabolic Flight (Projectile Motion)
Projectile Motion
Projectile - object thrown or launched and does not move under its own power
The combination of initial forward velocity and the downward force of gravity causes things to travel in a curved path (parabola) Ex: throwing a ball, a ski jump, a cannon ball being shot, punting a football
If it wasn’t for gravity, the ball would continue to travel in a straight line due to Inertia
Videos
1st Law – NFL2nd Law - NFL3rd Law - NFL
Newton’s 2nd Law of Motion
Newton’s 2nd Law
Force = mass x acceleration
Acceleration = The rate something speeds up, or slows down
Force – let’s review!
How hard something is pushing or pulling
Measured in “Newtons” (N)
Ex. I pushed the ball up the hill with 10 N of force
Units for 2nd Law Problems
For our purposes, we will only be using the following units (standard SI units) when solving Newton’s 2nd Law related problems:FORCE = Newtons (N)MASS = kilograms (kg)ACCELERATION = m/s/s (meters per second
per second)
F = m x a
What happens to the force if:You increase the acceleration?You increase the mass?
Examples
Two students are in a baseball game. The first student hits a ball very hard and it has a greater acceleration than the second student who bunts the ball lightly.
A soccer ball accelerates more than a bowling ball when thrown with the same force.
Example 1 – Prove it mathematically!
Two students are in a baseball game. The first student hits a ball very hard and it has a greater acceleration than the second student who bunts the ball lightly.
Baseball has a mass of 0.15kg.
Student A hits very hard with a Force of 1000N
Student B bunts with a Force of 100N
a = F ÷ mStudent A
a = 1000 ÷ 0.15 = 6666.67 m/s/sStudent B
a = 100 ÷ 0.15 = 666.67 m/s/s
Example 2 – Prove it mathematically!
A soccer ball accelerates more than a bowling ball when thrown with the same force.
Soccer ball mass = 0.5kgBowling ball mass = 6.5kgForce = 50NSoccer ball
a = 50 ÷ 0.5 = 100 m/s/sBowling ball
a = 50 ÷ 6.5 = 7.7 m/s/s
Newton’s 2nd Law proves that different masses accelerate to the earth at the same rate, but with different forces.
Objects that are falling accelerate to the ground at the same rate (9.8 m/s/s) When the upward force of air resistance = the downward force of gravity pulling on the object, it stops accelerating.
We call this Terminal Velocity
However, because of the 2nd Law we know that they don’t hit the ground with the same force.
Objects that are falling accelerate to the ground at the same rate (9.8 m/s/s) When the upward force of air resistance = the downward force of gravity pulling on the object, it stops accelerating.
We call this Terminal Velocity
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 m/s/s9.8 N = 1 kg x 9.8 m/s/s
Can a cat survive a fall from a plane?
There’s another reason besides a cat’s natural instincts to detect acceleration…
Cat’s average mass = 9 kgHuman’s average mass = 75 kgAcceleration due to gravity = 9.8 m/s/sWho hits the ground with more FORCE?
Example:
A boulder has a mass of 8 kg, and you push it so that it accelerates 3 m/s/s. How much force did you push it with?
Example:
You push your friend in the next desk with a force of 18 Newtons. They have a mass of 2 kg. How much will they accelerate?
Example:
Your parents ask you to help the neighbors move. They ask you to pull a box into the truck. You pull with exactly 35 Newtons of force, and the box accelerates 5 m/s/s. What was the mass of the box?
Newton’s 3rd Law of Motion
Newton’s 3rd Law
Every action has an equal and opposite reaction
Example:Action = You kick a soccer ballReaction = The soccer ball kicks you!
In other words…
“This means that for every force there is a reaction force that is equal in size, but opposite in direction. That is to say that whenever an object pushes another object it gets pushed back in the opposite direction equally hard.”
Examples
Fish through water - water goes back, fish goes forward
Bird flying - wings push down, air pushes up
Fire hose - water comes out, hose pushes back
Balloon
Rocket Example
The rocket's action is to push down on the ground with the force of its
powerful engines, and the reaction is that the ground pushes the rocket
upwards with an equal force.
Gravity Example
More Examples
Space shuttle lifting off
Airplane flying through the air
EVERY force has a reaction force