Torque, Momentum, Impulse,, Energy 2-9 is Torque 10-16 is
momentum
Slide 2
Weight vs. Mass Weight is mass times gravity W= mg or F w =mg
Mass in kilograms Gravity is 9.8m/s 2 on earth Mass how much stuff
or matter you are made up of. Mass is also measure of your
inertia.
Slide 3
YOUR WEIGHT? ON VARIOUS PLANETS
http://www.exploratorium.edu/ronh/weight/
Slide 4
Assignment: Two forks.
Slide 5
Center of Mass: The point in an object where all of its mass
balances around. When a force is exerted on an object outside of
its center of mass, it will rotate.
Slide 6
Hammer: Center of Mass
Slide 7
Two bodies with the same mass orbiting a common barycenter
similar to some asteroids (Antipoe 90) Two bodies with a difference
in mass orbiting a common barycenter similar to pluto- charon
system Two bodies with a major difference in mass orbiting a common
barycenter internal to one body (similar to the EarthMoon system)
Two bodies with an extreme difference in mass orbiting a common
barycenter internal to one body (similar to the SunEarth system)
Two bodies with the same mass orbiting a common barycenter,
external to both bodies, with eccentric elliptic orbits (a common
situation for binary stars)
Slide 8
Torque Torque is a measure of how much a force acting on an
object causes that object to rotate about an axis. Formula = Fr
=torque (N-m) F=Force (N) r = distance from axis (m)
Slide 9
Opening a Door Its harder to open a door closer to its hinges.
Its easier to open a door far away from its hinges because r is
greater and there is more Torque.
Slide 10
EXAMPLES OF TORQUE SEASAWSCROWBARS --Fulcrum
Slide 11
PHET PHYSICS TORQUE SEASAW PHYSICS To balance a seesaw, the
torque on one side must equal the torque on the other side.
Problem: A 150lb adult sits 4 feet from the center of a seesaw.
Where must a 100lb person sit to balance equally? TORQUE
Slide 12
Torque Lab Students will be given a ring stand and clamps,
rubber bands and several masses. They set up and sketch the
problems on the next page. Use dowels or wood rulers to create a
multi- layered balanced torque system.
Slide 13
Place a a 200g mass 10cm from the axis of rotation. Where would
you put a 100g mass on the other side to balance it? Place a 200g
mass 20cm from the axis of rotation and a 100 mass 10cm from the
axis of rotation. Where would you have to put another 100g mass to
balance it? Place the mystery mass object 30cm from the axis of
rotation.
Slide 14
Torque Problem
Slide 15
Jenga Block Game 1.No glue! Blocks have to be placed and
supported entirely by their own weights. 2.Only one block per
level. We're making a skewed tower. 3.All blocks are of the same
shape, weight, and are of uniform density. 4.Must stand for 30
seconds. 5.2 nd attempt: you may use 10 pennies and two rubber
bands.
Slide 16
MOMENTUM
Slide 17
Momentum and Collisions Momentum can be defined as "mass in
motion." If any object with mass is moving, then it has momentum
p=mv p=momentum (kg-m/s) m=mass (kg) V= velocity (m/s)
Slide 18
Momentum & Collisions! Newtons CradleBilliards
Slide 19
Conservation of Momentum The total momentum of two or more
objects before a collision is the same as the momentum of the
objects after a collision.
Slide 20
1) Calculate the momentum for the following objects: a)A 75kg
speed skater moving forward at 16m/s b)A 135 ostrich running north
at 16.2m/s c)A 5.0kg baby on a train moving eastward at 72m/s d)A
48.5kg passenger seated on a train that is stopped. 2) Calculate
the velocity of a 0.8kg kitten with a forward momentum of 5kg-m/s.
3) Calculate the momentum of a 6.0kg bowling ball moving at 10m/s
down the alley towards the pins.
Slide 21
1.A one kilogram ball traveling at 1m/s hits a another
stationary 1kg ball. The ball moving initially stops. What happens
to the ball that was originally stationary? 2.A two kilogram ball
moving at 2m/s hits a stationary 1.5 kg ball. After the collision
the two kilogram ball is moving at 1m/s. How fast is the 1.5kg ball
moving? 3.A toy car with a mass of 0.5kg is moving with a velocity
of 3m/s and it smashes into and sticks to another car with a mass
of 1kg. What is the velocity of the cars after the collision?
Slide 22
Momentum A 500kg canon at rest fires a 10kg ball at 100 meters
per second. What happens to the canon?
Slide 23
Work Energy is the ability to do work. Work is the amount of
force used to move an object a given distance. Formula for Work is
W = Fd F = force in Newtons d = distance in meters. The unit for
energy and work is the joule.
Slide 24
Working Hard or Hardly Working Energy is the ability to do
work. Work is the amount of force used to move an object a given
distance. Formula: W = Fd F = force in Newtons d = distance in
meters. The unit for work is the joule.
Slide 25
Lifting Objects: Work done against gravity W = mgh Height
object raised (m) Gravity (m/sec 2 ) Work (joules) Mass (g)
Slide 26
Mr. Sapone who is super awesome and super strong deadlifts a
220kg barbell a total distance of 0.7meters before dropping it. How
much work did he do?
Slide 27
If you carry a 800N could 10 meters across a room, how much
work did you do?
Slide 28
If you carry an object at a constant velocity you do no work on
the object because there is no net force in that direction. You
might be tired but you didnt do any work.
Slide 29
Two cases: No work done.
Slide 30
A crane uses an average force of 5,200N to lift a girder 25m.
How much work does the crane do on the girder? An apple weighing 1N
falls distance of 1m. How much work is done on the apple by the
force of gravity? A bicycles breaks apply 125N of frictional force
to the wheels as the bike moves 14.0m. How much work do the breaks
do? A mechanic uses a hydraulic lift to raise a 1,200kg car 0.50m
off the ground. How much work does the lift do on the car?
Slide 31
Work against gravity: W=mgh 1A crane lifts a steel beam with a
mass of 1,500 kg. Calculate how much work is done against gravity
if the beam is lifted 50 meters in the air. 2How much time does it
take to lift the beam if the motor of the crane can do 10,000
joules of work per second?
Slide 32
Power Power is the rate at which work is done. Power is work
divided by time. P = W/t (J/s) 1 J/s = Watt
Slide 33
P = W/t W = Fd P = Fd/t 746watts is one horsepower
Slide 34
Power Problems
Slide 35
Quick Lab: Calculate your Power 1.Convert your body weight into
Newtons by dividing by ~4.5_____ 2.Measure the time it tales you to
run up the steps in seconds ____ 3.Measure the height in cm of one
step____ and multiply that by the total number of steps____ to get
the total height ________. Convert that into meters by dividing by
100__________ 4.Calculate your power by multiplying your body
weight in Newtons by the height of the steps in meters______
5.Divide your Power by 746 to convert it into horsepowerc____
Slide 36
Kinetic Energy The energy of motion. KE = 1/2 mv 2 m = mass of
the object v = objects velocity
Slide 37
KE Sample Problems A tomahawk missile has a velocity of 250m/s
and a mass of 1300kg, calculate its Kinetic energy. A 9mm bullet
with a mass of 0.08kg has a velocity of 400m/s, what is its Kinetic
energy? Which one has greater kinetic energy? A 1000kg car moving
90Mi/h (40m/s) or a 36,000kg 18 wheeler going 30Mi/h (13.4m/s)
Slide 38
Potential Energy: Stored energy. Elastic Potential Energy U =
kx2 (Spring or elastic potential energy) k = spring constant x =
distance stretched in meters A stretched spring stores energy
Slide 39
Potential Energy: Stored energy. Gravitational Potential Energy
PE = mgh m = mass of object g= gravitational acceleration height
from surface in meters
Slide 40
Potential Energy Problems A 60kg woman is in a helicopter at a
height of 2500 meters. What is her potential energy? A 0.4kg apple
is hanging from a tree 3.4 meters from the ground. What is its
potential energy? What height must I raise a 20kg object to in
order for it to have 1000 joules of potential energy?
Slide 41
Conservation of Energy Energy is neither created or destroyed.
If you cut the object to the left all of its potential energy will
turn into kinetic energy before it hits the floor.
Slide 42
Conservation of Energy PE (top) = KE (bottom)
http://phet.colorado.edu/en/simulation/energy-skate-park
Slide 43
PE-KE Problems If I throw a 1kg object out of a window 15
meters off the ground. What will its velocity be just before
impact? In the figure on the right, label from greatest to least,
potential energy and kinetic energy.