Download Newton`s Laws/ Simple Machine Notes

Describing Motion
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Motion- occurs when an object changes position relative to a reference point
DISTANCE vs. DISPLACEMENT
Distance – how far an object has traveled
Displacement – distances and direction of an object’s change in position
from starting point
SPEED
Speed – the distance an object travels per unit time – rate of change in
position
Avg. Speed (v) = total distance (d) / total time (t)
V=d/t
Type of speed
Description
Example
INSTANTANEOUS
Speed at any given
point in time
Driving a car and
looking down at the
speedometer
AVERAGE
Total distance traveled
Taking a road trip
divided by total time
CONSTANT
Speed that does not
vary
GRAPHING MOTION
Putting car in cruise
control
Acceleration
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Velocity (v) – includes speed of an object and the direction of its motion
Q: what is the difference between speed and velocity?
A: Velocity includes directions where speed does NOT.
Acceleration (a)- rate of change of velocity
Acceleration occurs when an object changes speed, its direction, or both
Calculating Acceleration
Acceleration (meters/ seconds) = change in velocity (m/s)
Time (s)
note: change in velocity = final velocity – initial (starting) velocity
Positive acceleration: The plane is speeding up.
Negative acceleration: The bike is slowing down.
Motion and Forces
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Force – a push or pull applied to an object
Net Force – when two or more forces act on an object at the same time
Friction- the force that opposes the sliding motion of two touching surfaces
Type of Friction
Description
Example
Static
Friction in which two
surfaces are not moving
past each other
Pushing a fridge across
a floor
Sliding
Friction where two
surfaces past one
another
Sledding down a hill
Rolling
Friction between a
rolling object and
surface it rolls on
Skateboard moving on
ground
Fluid
Friction when object
moves through fluid,
meaning either a liquid
or a gas
Skydiving
Friction is caused by microscopic bumps on surfaces called microwelds.
Air Resistance- friction- like force that opposes motion of objects that move
through air – depends on speed, size, and shape of object
Newton’s Laws of Motion
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Newton’s First Law of Motion
An object in motion stays in motion, or an object at rest stays at rest until
an unbalanced net force acts upon it
Inertia: tendency of an object to resist any change in its motion
Newton’s Second Law of Motion
A net force acting on an object causes the object to accelerate in the
direction of the force
Force = mass times acceleration
Newton’s Third Law of Motion
For every action (or force), there is an equal and opposite reaction (or force)
Momentum- property of a moving objecting resulting from its mass and
velocity
Momentum (p) = mass times velocity
Gravity
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Gravity – any two masses that exert an attractive force on each other
Gravity depends on mass and distance between objects
Weight – gravitational force exerted on an object; measured in units called
Newtons
The greater the objects mass, the stronger the gravitational force on it
Projectile Motion
Projectile – anything that is thrown or shot through air
A projectile follow a curved path and has:
Horizontal Motion
and
Vertical Motion
Motion parallel to Earth’s Surface
Motion perpendicular to Earth
Centripetal Force
Centripetal acceleration – acceleration toward the center of a curved or
circular path
“Centripetal” means toward the center
Centripetal Force – force acting toward the center of a curved or circular
path
The Nature of Energy
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Energy – the ability to cause change
Forms of energy include:
- Electrical
- Thermal (heat)
- Chemical
- Radiant (light)
Kinetic Energy – energy in the form of motion
KE depends on mass and velocity of moving object.
Example of KE: Going down a slide
Potential Energy – energy that is stored
Example of PE: waiting at top of slide
Elastic Potential Energy- energy stored by something that can
stretch or compress, such as a rubber band or a spring
Chemical Potential Energy- energy stored in chemical bonds
A glass of milk has CPE until you drink it then calories are used as
energy for your body
Gravitational Potential Energy- anything that can fall has stored
GPE
A ball on a ledge has GPE
Conservation of Energy
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Energy can be transformed from one form to another
 Ex. Light Bulb
Light energy
Thermal energy
Mechanical Energy – total amount of kinetic energy and potential energy in a
system
ME= PE + KE
Point A: PE Maximum, KE = 0
Point B: KE , PE
Point C: KE , PE
Point D: PE Maximum, KE = 0
* : Total Mechanical Energy
The Law of Conservation of Energy- Energy may change form, but it cannot
be created nor destroyed in ordinary conditions
Work
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Work – transfer of energy that occurs when a force makes an object move
For work to be done, something has to move AND the motion must be in the
same direction as the force.
When work is done, a transfer of energy always occurs.
Calculating Work:
Work (Joules) = Force (Newtons) times Distance (meters)
W= F * D
Ex. You push a wheelbarrow with a force of 100N. You moved the
wheelbarrow 5m. How much work did you do?
W= F * D
W= (100N) * (5m)
W= 500 J
Power- the rate at which work is done.
Calculating Power:
Power (Watts) = work (J)
Power equals work divided by time
Time (s)
Ex. You do 900J of work pushing a fridge. It took 5 seconds. What was your
power?
P = W/T = 900J/ 5s = 180 J/s = 180 watts (w)
Work: transfer of energy that occurs when a force makes an object move
Unit: Joules
W (J) = F x D
Distance: the distance an object moves from one place another
D (m) = W/F
Unit: Meter
Force: Push or pull
Unit: Newtons
F (N) = W/D
Using Machines
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Machine – device that makes doing work easier
Machines make work easier by easing the force that can be applied to an
object
Two force are involved when a machine does work
(Fin) Input Force
the force applied to
machine
Output Force (Fout)
the force applied by machine
Picture of Hammer
Mechanical Advantage – the ratio of the output force to the input force
Mechanical Advantage (MA) = Output force (Newtons)
Input force (Newtons)
MA = Fout
Fin
Efficiency- measure of how much work put into a machine is changed into
useful work by the machine
Machines can be made more efficient by reducing friction.
Increasing Force: Machines can make work easier by increasing the force
that can be applied to an object
Increasing Distance: Machines can make work easier by increasing the
distance over which a force is applied
Changing Direction: Machines can make work easier by changing the
direction of an applied force
Simple Machines
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Simple Machine – Machine that does work with only one movement of the
machine
Lever:
Bar that is free to pivot around a
fixed point (fulcrum)
Pulley
Grooved wheel with a rope chain or
cable running along groove
1st Class Lever: fulcrum is between input
Fixed Pulley: attached to something that
force and output force
doesn’t move (directional advantage)
2
Moveable Pulley: one end of the rope is
nd
Class Lever: output force(Load) is
between fulcrum and input force
fixed and the wheel is free to moved
3
(mechanical advantage)
rd
Class Lever: input force (Effort) is
between fulcrum and output force
Block and Tackle: system of pulleys
consisting of fixed and moveable pulley
Wheel and Axle:
Consists of an axle attached to
center of a larger wheel so that the
wheel and axle rotate together
Inclined Plane:
Sloping surface, such as a ramp that
reduces the amount of force required
to do work
The Screw:
Inclined plane wrapped around a
cylindrical post
The Wedge:
An inclined plane with one or two
sloping sides (Knife)
Compound Machine: Two or more simple machines that operate together
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