Download File - We All Love Science

Unit 2: Gravity and Motion
Mr. Ross Brown
Brooklyn School for Law and
Technology
In this unit we will learn:
• What is inertia and how does it affect me?
• How force affects speed or motion.
• How to estimate the size and direction of a
force.
• The importance of Newton’s three laws of
motion.
Aim: How does Inertia Affect the
Motion of Cosmic Bodies?
• Date: 1 April 2016
• Do now: If you’re a passenger in a car, what
happens to you when the driver slams on the
brakes? Why do you wear a seat belt? What
happens to a bag of groceries on the back
seat?
Aim: How does Inertia Affect the
Motion of Cosmic Bodies?
• Inertia: the tendency of a body at rest to stay
at rest, or a body in motion to keep moving in
a straight line at a constant speed.
• Galileo’s experiment
• Newton’s first law of motion: a body continues
in a state of rest or motion in a straight line at
a constant speed unless made to change that
state by forces acting on it.
Newton’s First Law of Motion
• A body continues in a state of rest or motion
in a straight line at a constant speed unless
made to change that state by forces acting on
it.
• Often referred to as the:
Law of Inertia
Homework, 8 October 2015
• What does Newton’s First Law of Motion tell
you about the difference between motion in a
straight line and motion along a curve? Be
prepared to discuss in class tomorrow.
Aim: How does Newton’s first law
explain orbital motion?
• Date: 4 April 2016
• Do now: Think about the amusement park
ride where you’re pressed back against the
wall of a cylinder and can’t move. Explain the
forces at work.
Aim: How does Newton’s first law
explain Orbital Motion?
• Newton’s Cannon
• Why does the cannonball not continue in a
straight line?
• The balance between inertia and gravity
maintains the orbit.
• With no force – straight line
• With force (gravity) – curved line
• Inertia keeps it in motion
Aim: How do acceleration and
mass affect motion?
• Date: 5 April 2016
• Do now: If you’re walking down the hall in a
straight line, minding your own business, how
do other students interfere with your motion?
In what ways do they bother you when you
simply want to get to class?
How do forces act on objects in
motion?
• Motion: a change in the position of an object
• Inertia: uniform motion (constant speed and
direction)
• Acceleration: any change in speed or direction
Uniform motion: Same
speed and direction
Acceleration: A change
in speed (faster or
slower)
Acceleration: A change
in direction
How does a force affect an object’s
acceleration?
• Acceleration is proportional to force applied,
i.e., larger forces produce larger accelerations.
How does an object’s mass affect
its response to a force?
• Mass: a measure of an object’s inertia
• For the same force an object’s acceleration
decreases as its mass increases
Which will coast better?
How does an object’s mass affect
its response to a force?
• When a Force, F, acts on an object whose
mass is m, it produces an acceleration, a.
• F=ma
• Therefore, a=F/m
Newton’s Second Law of Motion
• The acceleration of a body is proportional to
the net force exerted on it, but inversely
proportional to the mass of the body.
Homework #6
• 5 April 2016
• Use Newton’s Second Law of Motion to
explain why smaller cars get better gas
mileage than larger ones.
Aim: What happens when bodies
exert forces on each other?
• 6 April 2016
• Do now: How does a rocket lift off and then fly
through space?
What happens when bodies exert
forces on each other?
• Newton’s Third Law of Motion
• Also called the Law of Action-Reaction
• When two objects interact, they create equal
and opposite forces on each other.
Newton’s Third Law of Motion
How do we calculate gravity?
• 7 April 2016
• Do now: What information (data) would you
need in order to calculate the force of gravity
between two objects?
How do we calculate gravity?
• The Law of Gravity
• Every mass exerts a force of attraction on
every other mass. The strength of the force is
directly proportional to the product of the
masses divided by the square of their
separation.
How do we calculate gravity?
d
d2
Why else do we care about
gravity?
• Surface gravity: the rate at which all objects
accelerate downward similarly. This is the
gravitational attraction of a planet’s or star’s
surface. Determines weight.
• Your weight on the Earth is roughly 6 times
your weight on the moon because the Earth’s
mass is so much greater.
How do we get past earth’s orbit
on a rocket?
• Escape velocity: the speed an object must
have to be able to move away from a body
and not be drawn back by its gravity.
Homework #6, part 2
• 7 April 2016
• If you weigh 110 pounds on the earth, do you
weigh 110 pounds on the moon? Why or why
not?