Download Unit 2

Unit 2
Pages 248-249, 272-277, and 280-287
Gravity
• Sir Isaac Newton
• Why do objects fall?
• A force pulls objects downward, towards
the center of the Earth
• All objects are attracted to each other to
some degree due to gravity
Mass
• Amount of mass effects force of gravity
• Larger the mass, greater the
gravitational force it exerts
• An apple’s center is attracted to Earth’s
center
• Earth has more mass, so the apple
moves and not Earth
Distance
• The force of gravity decreases as
distance increases
• Closer together the objects are, more
force they exert on each other
• Farther apart they are, the less force
they exert
Motion
• Change in an object’s position
• Speed = distance divided by time
• Average speed = total distance divided
by time
• Velocity = involves speed and direction
• Acceleration = change in velocity
divided by time
Speed
• My dog runs 50 meters in 5 seconds.
• What is my dog’s speed?
• What are the units?
Average Speed
• It takes you 3 hours to travel 50 miles to
Omaha.
• What was your average speed?
• What are your units in this problem?
• What do we usually want our units of
speed to be?
Average vs. Instantaneous
Speed
• Average speed is how fast you traveled
for the entire trip.
• Instantaneous speed is how fast you
are going at the moment that the police
officer uses his radar gun on your
vehicle and gives you a speeding ticket.
Acceleration
• My dog began his walk at 10 meters per
second. 2 hours later, he was walking
at 2 meters per second.
• What was his acceleration?
• What are the units?
Momentum
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Mass x velocity
Mass will be in grams, kg, mg, etc.
Velocity will be in meters per second
Conservation of Momentum = total
momentum of system always stays the
same
Momentum
• The 2000 kg truck is driving at 30
meters per second.
• What is the truck’s momentum?
• What are the units?
Newton’s 1st Law of Motion
• An object will remain at rest or move at
a constant speed in a straight line
unless acted upon by a force
• Also known as the Law of Inertia
• Inertia is the resistance to change in
motion.
• It is hard for en elephant to stop quickly
because it has a lot of inertia carrying it
forward.
Newton’s 2nd Law of Motion
• The force acting on an object is equal to
mass of the object times the
acceleration
• Force = mass x acceleration
• F= m x a
• Mass must be in kilograms
• Acceleration must be in m/s2
Calculating Force
• A 10 kg object accelerates at a rate of
45 m/s2.
• Calculate its force.
• What are the units?
• A new unit you will use is Newtons!
• 1 N = 1 kg x m/s2
Newton’s 3rd Law of Motion
• For every action force, there is an equal and
opposite reaction
• When a rocket is launched into space, its jets
must first ignite its fuel pushing down against
the ground.
• This is the action.
• The force of the explosion causes the rocket
to fly upward.
• This is the reaction.