Transcript Newton`s Second Law of Motion

Newton’s Second Law of
Motion
Take notes on page 47 of your
notebook
• Newton’s first law tells
us that this soccer
ball will remain at rest
until a force acts on it.
• Newton’s second law
tells us that force
causes acceleration
• The acceleration also
depends on mass.
• Newton’s first law tells us
that this soccer ball will
remain in motion until
acted on by a force.
• Newton’s second law tells
us that the force of the
man’s face caused the
ball to accelerate.
(acceleration is a change in speed or direction.)
• It also tells us that the
acceleration depends on
the mass of the ball.
(mass is the amount of matter)
Answer on page 46
1. What must this little boy do to break
the same board as a large man?
(Hint: F = m x a )
Let’s say it with math!
• Force equals mass times acceleration
• F=ma
• Newtons = kilograms x meters per second
squared
• Example: 500N = 100 kg x 5 m/s2
Solve this problem
Write on page 46 of your notebook
2. A company uses a ramp to slide a box of
parts to a shipping area. Each box weighs
10 kilograms. When sliding down the
ramp, the box accelerates at a speed of
0.1 m/sec2. What is the force acting on the
box?
Mass vs Weight
• Mass is the amount of matter in an object
• The mass of something remains the same
on the earth, the moon, or even in the
weightless vacuum of space
• Weight is a force created by gravity
• The weight of an object depends on the
gravity of the planet and the mass of the
object.
Mass vs weight
Mass is measured in grams or kilograms
(or
micrograms, or picograms, or femtograms…anything with grams!)
Weight is measured in Newtons, because
it is a force.
Answer these questions
Answer on page 46 of your notebook
An astronaut has a mass of 75 kg.
3. What is her mass on the moon?
4. What is her mass in space?
5. What is her weight on the earth?
6. What is her weight on the moon?
7. What is her weight in space?
HINTS: The acceleration of the earth’s gravity is 9.8 m/s2
The acceleration of the moon’s gravity is 1.6 m/s2
Some types of forces
•
•
•
•
Gravity
Electromagnetic
Nuclear forces
Friction
Friction
Rolling friction
Viscous friction
• Frictional force Opposes motion
• Friction occurs when two
surfaces move against each other
Sliding friction
Air friction
Equilibrium
• When you add up all the forces on an object, you get a
NET Force.
• When the net force is not zero, motion occurs
• When the net force is zero, no motion occurs. This is
called equilibrium
The force of gravity is equal to the
force of the sliding friction between
the man’s shoes and the rock and
the force of the rock pushing up on
the man. His forces are in
equilibrium.
Last assignment!
On page 46, make a Venn diagram of mass
and weight.
Coming Events
• Newton’s Third Law of Motion &
Momentum
• Fan Cart Gizmo (What’s Mass Got To Do
With It?)
• Lab with the cars and ramps
• Make a Newton’s Laws powerpoint