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NEWTON’S
LAWS OF
MOTION
Potential vs. Kinetic Energy • Kinetic energy = moving energy. Increases with
speed.
• Potential energy = stationary. Increases with
height.
Where is Potential Energy the greatest?
Where is Kinetic Energy the greatest?
Balanced and Unbalanced Forces
- Balanced forces - forces that are equal but in
opposite directions, canceling each other.
- Unbalanced forces - if one force is greater than
another, a change in motion will result
- Combining forces – the combination of all forces
acting on an object is called a NET FORCE
- *Force is measured in Newtons*
50N 50N
Forces
Identifying forces:
Forces
Identifying forces:
Forces
Identifying forces:
Forces
Hammer and Feather on the Moon?
At the end of the last Apollo 15 moon walk (July 1971),
Commander David Scott held out a geologic hammer
(1.32-kg aluminum) and a feather (0.03-kg falcon feather)
and dropped them at the same time. Because they were
essentially in a vacuum, there was no air resistance and
the feather fell at the same rate as the hammer, as Galileo
had concluded hundreds of years before - all objects
released together fall at the same rate regardless of mass.
http://nssdc.gsfc.nasa.gov/planetary/lunar/apollo_15_feather_drop.html
What will happen? - Clothes on the floor of your room.
- A ball rolling across the gym floor.
- A tennis ball flies through the air after you hit it.
- The car you are riding in suddenly stops.
- You left your sonic drink on the roof of the car
and the driver stomps on the gas.
- The driver of the car takes a sudden turn.
So you’re saying that the objects at rest stay at rest, the
moving objects stay moving and they also resist changing
their motion?
Newton’s 1st Law of Motion An object at rest will stay at rest unless acted on by an
unbalanced force, and an object in motion will stay in
motion unless acted on by an unbalanced force.
For your notes:
- Newton’s 1st Law - An object at rest will stay at rest, an
object in motion will stay in motion unless acted on by an
unbalanced force.
• Whether an object is moving or not, it resists any change
to its motion. Galileo’s concept of the resistance to a
change in motion is called inertia.
For your notes:
- Inertia is the tendency of an object to resist a change in
motion.
Newton’s 1st Law of Motion
Newton’s 1st Law (aka Law of Inertia)
Inertia says that objects at rest want to stay at rest and objects in motion want to stay in motion – they resist changing motion.
You move forward in your seat when a car stops suddenly. When the car stops, inertia tried to keep you moving forward. A force, such as the pull of a seat belt, is required to change your motion.
Furthermore, objects want to remain in motion in a straight line. This means that objects want to resist changes in speed or direction.
When a car is turning a corner, a driver’s body is usually thrown outward causing them to shift in their seat. This shift of the pull outward is due to inertia.
Inertia The inertia of the objects on the table keeps them from
moving.
Inferring Why should the girl use a slippery tablecloth?
Newton’s 1st Law (aka Law of Inertia)
Inertia Depends on Mass
Newton noticed a special relationship between the mass and the inertia of an object. He concluded that more the mass an object has, the more it resists a change in motion (more mass = more inertia).
For example: Which is harder to move?
An adult on a swing vs. a small child
Why?
An empty aquarium vs. one full of water
Why?
The greater the mass of an object is, the greater its inertia, and the greater the force required to change its motion.
add to notes under inertia
Newton’s 1st Law (aka Law of Inertia)
• Two trucks are traveling at the same speed towards each other. If truck A is big and it runs into small truck B, in what direction does small truck B go?
• A bouncy ball is thrown at a window and a baseball is thrown at a window both are thrown at the same speed. Which one will do more damage?
• You’re walking down the hallway and someone walks into you when you turn a corner. The next day the same person is running down the hall and runs into you when you turn the corner. Which day does it hurt more?
So, you’re saying that force depends on how big something is or how fast it’s moving?
What will happen?
Newton’s 2nd Law of Motion The acceleration of an object depends on the object’s mass
and on the net force acting on the object.
For your notes:
- Newton’s 2nd Law - acceleration of an object depends on
it’s mass and force acting on it.
Force = Mass x Acceleration
Newton’s 2nd Law of Motion
• Force is measured in Newtons (N)
• Acceleration is measured in meters per second squared
(m/s2)
• Mass is measured in kilograms (Kg)
For your notes:
Force – Newtons (N)
Mass – Kilograms (Kg)
Acceleration – meters per second squared (m/s2)
• If mass equals 200 kg and the acceleration
equals 3 m/s2 you can plug these into the
equation F = MA. It would look like this:
F = MA
F = 200 kg x 3 m/s2
F = 600 N
Newton’s 2nd Law of Motion
• What if mass is 10 kg and acceleration is 7
m/s2?
F = MA
F = 10 kg x 7 m/s2
F = 70 N
Newton’s 2nd Law of Motion
• If a 30 kg sand bag is dropped from a hot air
balloon, what will its force be when it hits the
ground? (the acceleration of gravity is 9.8 m/s2)
F = MA
F = 30 kg x 9.8 m/s2
F = 294 N
Newton’s 2nd Law of Motion
- If you and your friend are both on skates and
you push on each other.
What will happen?
- If you and your friend are both on skates and
you push on each other.
- Sitting in a kayak you take a paddle and push
against the water.
What will happen?
- If you and your friend are both on skates and
you push on each other.
- Sitting in a kayak you take a paddle and push
against the water.
- You hit a volleyball.
What will happen?
So you’re saying that for
every force there is an
equal and opposite
force?
Newton’s 3rd Law of Motion If one object exerts a force on another object, then the
second object exerts a force of equal strength in the
opposite direction on the first object.
For your notes:
- Newton’s 3rd Law – for every action there is an equal and
opposite reaction
- If a tennis racket hits a tennis ball with a force of 2,500 N, what
force does the tennis ball put back onto the racket?
Newton’s 3rd Law of Motion
- If a tennis racket hits a tennis ball with a force of 2,500 N, what
force does the tennis ball put back onto the racket?
- If a golf club strikes a golf ball with a force of 9,000 N, what
force does the tennis ball put back on the club?
Newton’s 3rd Law of Motion
- If a tennis racket hits a tennis ball with a force of 2,500 N, what
force does the tennis ball put back onto the racket?
- If a golf club strikes a golf ball with a force of 9,000 N, what
force does the tennis ball put back on the club?
- Why is the golf ball deformed in this picture?
Newton’s 3rd Law of Motion
- If a tennis racket hits a tennis ball with a force of 2,500 N, what
force does the tennis ball put back onto the racket?
- If a golf club strikes a golf ball with a force of 9,000 N, what
force does the tennis ball put back on the club?
- Why is the golf ball deformed in this picture?
- If the forces are equal then why doesn’t the a baseball bat fly
as far as the baseball (in the opposite direction)?
Newton’s 3rd Law of Motion
- All 3 laws are at work all the time. We can apply all 3 laws
to one situation:
Newton’s 3 Laws of Motion
Some aid organizations, like the Red Cross,
deliver supplies to hard to reach people by
parachuting them down.
1. What forces are working on the parachute?
2. Draw AND label those forces.
3a. Is the object accelerating?
3b. Why or why not?
4. The supplies and parachute have a mass of
3,000 kg. Before the parachute was opened
is was accelerating at 9.8 m/s2. If the
parachute had failed, what would have been
the force the supplies would have hit the
ground with?
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