Transcript Module 1 Motion - Leon County Schools

Module 1
Motion
Speed, Velocity, & Acceleration
• What is Speed?
– Scalar Quantity (only have magnitude)
– How fast something is moving
– Distance traveled over time
– No direction
• Average speed is not instantaneous speed
Speed, Velocity, & Acceleration
• Distance
• Overall amount traveled
Speed, Velocity, & Acceleration
• Units of speed are derived units of
distance over time
• Speed (meters/second) =
distance (meters) /time (seconds)
Let’s Practice!!!!
• In a skateboarding marathon, the
winner covered 435 km in 36.75 h.
What was the winner’s average
speed?
• Florence Griffith Joyner set a world
record by running 200 m 21.34 s.
What was her average speed?
• An airplane is traveling at 400
mi/hr. It touches down at an airport
2000 mi away. How long was the
plane airborne?
Speed, Velocity, & Acceleration
• d/t graphs
– X-axis = time
– Y-axis = distance
(position)
• Speed on distance-time
graphs
– Think slope of line:
check it out
• Analyzing distance vs time
graphs
• ***Figure 7 in book***
Speed, Velocity, & Acceleration
What was the
object’s speed at 2 s?
What was the
object’s speed at 5 s?
How would describe
the motion of this
car?
What might you
predict the next plot
point to be?
Speed, Velocity, & Acceleration
What was the object’s
speed at 2 s?
The object stopped
during this time frame.
When did this happen?
Explain how you know.
What happened
between 9.8 s and 12
s? How do you know?
Speed, Velocity, & Acceleration
How is this graph
different?
How would you
describe the
motion of this
object?
Can we still
calculate speed??
How??
Speed, Velocity, & Acceleration
Speed, Velocity, & Acceleration
• Frame of Reference
• Motion is Relative to Frame of Reference
• You observe how other objects move by
comparing to that frame of reference
Speed, Velocity, & Acceleration
• Velocity
– Vector Quantity (magnitude and direction)
– Speed and direction
• Speed and Velocity are not the same
Speed, Velocity, & Acceleration
• Velocity
– Vector Quantity (magnitude and direction)
– Speed and direction
• Speed and Velocity are not the same
Speed
velocity
Scalar quantity
Vector quantity
How fast object is going with Speed and direction
respect to frame of reference
Ex. 50 miles per hour
Ex. 50 miles per hour, North
Let’s Practice!!!!
• A cart starting from rest travels a
distance of 3.6 meters northward in
1.8 seconds. What is the average
velocity?
• A car drives from Tallahassee to
Orlando. The distance is 830 km and
the drive takes 7.3 hrs. What is the
velocity of the car?
Speed, Velocity, & Acceleration
• Acceleration
• Rate at which velocity changes
– Speeding up (positive)
– Slowing down (negative)
– Changing direction
Speed, Velocity, & Acceleration
• Calculating Acceleration
Let’s Practice !!!!
• A roller coaster speeds up going down a hill
from 0 m/s to 11 m/s at the bottom of the hill.
If this occurs in 3 seconds, what is the
acceleration of the roller coaster?
• A cheetah is running at a velocity of 14 m/s
and slows to tackle a wildebeast to 2 m/s. If
the chase takes 4.2 seconds, what is the
cheetah’s acceleration?
Speed, Velocity, & Acceleration
• v/t graphs
– X-axis = time
– Y-axis = speed
– Analyzing speedtime graphs
– Think slope of line:
– ***Figure 16 in
book***
Speed, Velocity, & Acceleration
Find the acceleration
between 2-5
seconds.
How would you
describe this object’s
motion?
What would the next
plot point would be?
How do you know?
Speed, Velocity, & Acceleration
Find the acceleration
between 2-4
seconds.
Find the acceleration
between 7-9
seconds.
What is happening
between 4-7
seconds, How do you
know??
Speed, Velocity, & Acceleration
The Laws of Motion
• Force
– A push or a pull
– Measured in newtons
The Laws of Motion
• Balanced and Unbalanced Forces
The Laws of Motion
• Drawing and Interpreting Force Diagrams
The Laws of Motion
• Net Force
• Rules for Adding Forces
– Add forces in the same
direction.
– Subtract forces in opposite
directions
– Forces not in the same
directions\ or in opposite
directions cannot be
directly added together.
The Laws of Motion
• Friction
• Force that works against the motion of an
object
The Laws of Motion
• Newton’s 1st Law
– An object at rest will stay at rest and an object in
motion will stay in motion, unless an unbalanced
force acts on it.
– Break It Down: INERTIA – Things want to keep doing
what they are doing
– Inertia is directly related to mass.
The Laws of Motion
• Newton’s 2nd Law
– Acceleration of an object is directly affected by
the net force acting on it, and inversely by the
mass of the object
The Laws of Motion
• Newton’s 2nd Law
– Force (N) = mass (kg) x acceleration (m/s2)
Let’s Practice!!!!
• With what force will a car hit a tree if the car
has a mass of 3,000 kg and it is accelerating at
a rate of 2 m/s2?
• If a helicopter’s mass is 4,500 kg and the net
force on it is 18,000 N upward, what is it’s
acceleration?
The Laws of Motion
• Newton’s 3rd Law
– For every action (force applied) there is an equal
and opposite reaction (resulting force)
The Laws of Motion
• Momentum
– Mass of an object times its velocity
– A vector quantity (magnitude and direction)
– Momentum = mass x velocity
The Laws of Motion
• Conservation of Momentum
– Momentum remains constant for objects
interacting with one another in a system
Let’s Practice!!!!
Let’s Practice!!!!
Let’s Practice!!!!
The Laws of Motion
• Angular Momentum
– Deals with rotational
motion
– Is a product of mass and
velocity
– Depends on the distribution
of mass
– Angular mass (moment of
inertia)
Forces in Action
• 4 basic Forces
– Gravititational
– Electromagnetism
– Strong nuclear force
– Weak nuclear force
Forces in Action
• Gravitational
– Force of attraction between two objects
– Depends on mass and distance
– Weakest of the four forces
Forces in Action
• Gravity and Weight
– Measures the force of gravity on mass
– Weight and Mass are different things
Forces in Action
• Falling for Gravity
– Force of air friction
between falling
object and air
particles
– All objects regardless
of mass, experience
the same
acceleration when in
free fall
Forces in Action
• Electromagnetic Forces
– Forces occur when electric field interacts with
electrically charged particles
– Opposite charges attract, like charges repel
Forces in Action
• Strong Nuclear Forces
– Work at the atomic level
– Strong Forces
– Force that holds the nucleus of atom together
– Strongest of the 4 forces, short range
Forces in Action
• Weak Nuclear Forces
– Work at the atomic level
– Weak Forces
– Force responsible for particle decay (radioactivity)
Forces in Action
Force
Description of
the force
Particles
that
experienc
e the
force
Range of the Relative strength
force
of the force
Gravity
Attraction between
objects with mass
All particles
with mass
Infinity
Weakest of the 4
forces
Electromagnetism
Attraction or
repulsion between
electrically charged
particles
Electrically
charged
particles
Infinity
Second strongest of
the 4 forces
Strong nuclear
Hold’s the atoms
nucleus together
Atoms and
subatomic
particles
Short range
Strongest of the 4
forces
Weak nuclear
Governs nuclear
decay and
radioactivity
Atoms and
subatomic
particles
Short range
Second weakest of
the 4 forces
Energy
• Energy
– Ability to change or move matter
– Exists in many forms
• Potential
–
–
–
–
Nuclear
Elastic
Chemical
gravitational
• Kinetic
–
–
–
–
Electrical
Radiant
Thermal
Mechanical
Energy
Energy
• Energy Conversions
• Law of Conservation of Energy
– Energy cannot be created or destroyed, just
converted from on form to another
Energy
• Kinetic Energy
– energy of motion
– depends on mass and speed
• Kinetic Energy = ½ mass x speed (KE = ½ m v2)
KE (J) = ½ m (kg) X v (m/s)2
Energy
• What is the kinetic energy of a 136.4 kg
elephant moving at 34 m/s?
•What is the kinetic energy of a 22.7 kg boy on
his 45.5 kg bike rolling down a hill 25 meters
high at 7.21 m/s?
• Determine the kinetic energy of a 1000-kg
roller coaster car that is moving with a speed
of 20.0 m/s.
Energy
• • Potential Energy
• • stored energy(elastic,chemical,gravitational)
• Gravitational Potential Energy = mass x gravity
x height
• GPE (J) = m (kg) g (N/kg) h (m)
Energy
• What is the potential energy of a hammer that
weighs 25 N that is sitting on top of a ladder 5
meters high?
• What is the potential energy of a golf ball that
weighs 3.2 kg that is resting on top of a 1.2 m
high lab table?
• What is the potential energy of a golf ball that
weighs 3.2 kg that is resting on top of a 1.2 m
high lab table?
Energy
Energy
• Systems
Energy
– The container or entity
• Isolated system (neither energy or matter exchange)
• Closed system (energy can enter or leave, matter cannot)
• Open system (energy and matter exchanged freely)
Work & Power
• Energy is the ability to do work
• Force exerted over a distance
• Force must be in the same direction as the as
the distance
Work or Not Work
• A book falls off a table and free falls to the
ground.
• A waiter carries a tray full of meals above his
head by one arm straight across the room at
constant speed.
• A rocket accelerates through space.
• A teacher applies a force to a wall and
becomes exhausted.
Work & Power
• Calculating work
• Work = force x distance
• Work and force are directly related
Let’s Practice !!!!
• How much work is needed to push an object
that weighs 350 N a distance of 4 meters?
• A dancer lifts a 400 N ballerina overhead a
distance of 1.4 m. How much work is done?
• How much work is done by an applied force to
lift a 15-Newton block 3.0 meters?
• How much work is done on the wall by a
person pushing on the wall with 5600 N of
force?
Work & Power
• Negative Work
• A force acts on an
object to stop or slow
motion
• Force acts in direction
opposite of the motion
Work & Power
• Machine –
• Types of machines
– Simple machines
– Compound machines
• Two or more simple
machines
Work & Power
• How are machines useful?
• Increase speed
• Change direction of force
• Increase the force
• Mechanical advantage –
MA = output force (N)
input force (N)
Let’s Practice !!!!
• To pull a weed out of a garden, you can apply a
force of 50 N to the shovel. The shovel applies
a force of 600 N to the weed. What is the
mechanical advantage of the shovel?
• To lift a block on a movable pulley, you can
apply a force of 50 N to a rope. The rope
applies a force of 700 N to the block. What is
the mechanical advantage of the rope?
Work & Power
• Efficiency –
– Efficiency (%) =
output work (J)
input work (J)
– Machines can be made more efficient by
reducing friction
– All machines are less than 100% efficient
Work & Power
• You do 222 J of work pushing a box up a ramp.
If the ramp does 200 J of work, what is the
efficiency of the ramp?
• Find the efficiency of a machine that does 800J
of work if the input work is 2,000J.
Work & Power
•
•
•
•
Power
Rate at which work is done
Can be more work or work done faster
Hand saw versus power saw
Work & Power
•
•
•
•
Calculating power
Power (watts) = work(joules)/time (seconds)
Power and time inversely related
Power and work directly related
Let’s Practice !!!!
• A light bulb uses 300 J of energy in 4 seconds.
How much power does the light bulb require?
• What is the power of an electric toothbrush if
it can do 755.8 joulles of work in 75 seconds?
• An athlete is using the row machine in the
gym. She does 3245 joulles of work on the
oars in 72 seconds. What is her power
output?
Work & Power
• Power = work /time = force x distance
• Power = force x distance /time
• Power = force x velocity
• Power is related directly to velocity