Transcript 1st Day of Physics!!

Beginning Concepts and Basic Laws.
Aristotle- 384 B.C.-322B.C.
 The natural state of things is at
rest.
 Nothing moves unless you push it.
 Two kinds of motion
 Natural motion- straight up or
straight down.
 Violent motion- resulting from
an external push or pull.
Galileo Galilei= 1564 A.D.-1642 A.D.
 20 year study on objects in
motion.
 Published The Little
Balance, describing the
hydrostatic principles of
weighing small quantities.
 Became a teacher at the
University of Pisa in 1589.
 Conducted experiments
with falling objects and
produced his
manuscript Du Motu (On
Motion).
Galileo’s Concept of Inertia
 Except for the effects of air friction, objects of different
weights fell to the ground in the same amount of time.
 Although a force is needed to start an object moving, once
it is moving, no force is needed to keep it moving except
for the force needed to overcome friction.
Isaac Newton 1643-1727
 I. Every object in a state of uniform
motion tends to remain in that state
of motion unless an external force is
applied to it.
 II. The relationship between an
object's mass m, its acceleration a,
and the applied force F is F = ma.
 III. For every action there is an equal
and opposite reaction.
The relationship between mass and inertia
 Mass is the quantity of matter in an object
 Inertia involves an object’s resistance to change its
state of motion.
 The amount of inertia an object has depends on its
mass.
 GREATER MASS
GREATER INERTIA
Weight= Amount of gravitational pull on an object.
Force= a push or a pull
Weight and Mass are
proportional
 2x the mass= 2x the
weight
 ½ the mass= ½ the
weight
 Mass
is measured in
kilograms. (kg)
The 5 Step Process
 What do you know?
 What do you need to know?
 What formula will you use?
 Apply the formula
 Check your work and apply your units
Density= the measure of how
much mass occupies a given space.
 Equation for density
 D= Mass/Volume
 grams/cubic centimeters
(g/cm³)
 Kilograms
(kg/m³)
m= d x V
V= m / d
/ cubic meter
5 Step Process Word Problem
Example with Density
 Mandy held up a block of wood with a mass of 80
grams. Its volume was registered at 1.5 cm³. What is
the density of the block of wood?
 Step 1: mass= 80 g and volume= 1.5 cm³
 Step 2: density=?
 Step 3: D=m/v
 Step 4: D= 80 g / 1.5 cm³
 Step 5: D= 53.33 g/cm³
Standard Units for F, M, A
Acceleration is measured in meters
per second squared (m/s²)
Mass is measured in kilograms (kg)
Force is measured in Newtons (N)
1 Newton = 1kg/m/s²
What is weight?
 Weight = mg
 Weight is the force of gravity on a body.
 Near the surface of the Earth, g = 9.8 m/s2
Weight, Mass, and Gravity 5 Step
Word Problems
 If Mr. Jolly has a mass of 110 kg, and gravity is
registered at 9.8 m/s², what is his weight?
 What is the weight of Mr. Jolly on the moon where
gravity is measured at 1.6 m/s²?
 What is the weight of Mr. Jolly on Jupiter where the
gravity is measured at 26 m/s²
Force, Mass, Acceleration Formulas
to Know
5 Step Word Problems for Force,
Mass, and Acceleration
 1) Esaul allowed his hand to drop and strike the desk.
If his hand has a mass of 8kg and gravity is registered
at 9.8m/s², what would the force be when he struck
the desk?
 Tony threw his medicine ball into the wall at 2 m/s²
with 50 N of force. What was the mass of the ball?
 Madison rolled a 7kg bowling ball with 30 N of force
down an alley toward pins. What was the bowling
ball’s acceleration when it approached the pins?
Quick Review
1) What is another name for a kg/m/s²?
2) What is a unit for acceleration?
3) What is the formula for: a) force b) mass c) acceleration
4) Why are Aristotle, Galileo, and Newton important to the
field of physics?
5) List the 5 steps to a word problem below:
-1
-2
-3
-4
-5
What is Energy?
*Energy is defined as the
ability to do work.
Formula for work
Work = Force x Distance
 The unit of force is newtons
 The unit of distance is meters
 The unit of work is newton-meters
 One newton-meter is equal to one joule
 So, the unit of work is a joule
The concept of work.
Example problem- A spring extends by 0.05m when a
force of 9N is applied. Calculate the work.
Word Problems
 How much work does a mover have to
do if he needs to move a crate that
requires 15 N of force a distance of
100m?
 A rope is thrown over a beam, and one
end is tied to a 300 N bundle of lumber.
You pull the rope 2 m off the ground.
How much work is done?
Introducing Power
 Power is work over a period of time
 P= Force x distance / time
 Force is in Newtons, distance is in meters,
and time is in seconds.
 A unit of Power is measured in Watts (w).
Power word problems
1) How much power is used if a force of 35 Newtons is
used to push a box a distance of 10 meters in 5
seconds?
2) What is the power of a kitchen blender if it can
perform 3,750 joules of work in 15 seconds?
3) How much work is done using a 500-watt microwave
oven for 5 minutes.
History of Work
 Before engines and
motors were invented,
people had to do things
like lifting or pushing
heavy loads by hand.
Using an animal could
help, but what they
really needed were
some clever ways to
either make work easier
or faster.
Simple Machines
 Ancient people
invented simple
machines that
would help them
overcome resistive
forces and allow
them to do the
desired work
against those
forces.
Simple Machines
A machine is a device that
helps make work easier to
perform by accomplishing
one or more of the following
functions:
•transferring a force from one
place to another
•changing the direction of a
force
•increasing the magnitude of a
force
•Increasing the speed of a force
The six
simple
machines
are:







Lever
Wheel and
Axle
Pulley
Inclined
Plane
Wedge
Screw
Mechanical Advantage
 It is useful to think about a machine in
terms of the input force (the force you
apply) and the output force (force which
is applied to the task).
 When a machine takes a small input force
and increases the magnitude of the output
force, a mechanical advantage has been
produced.
Mechanical Advantage
 Mechanical advantage is the ratio of output force
divided by input force. If the output force is bigger
than the input force, a machine has a mechanical
advantage greater than one.
 If a machine increases an input force of 10 pounds
to an output force of 100 pounds, the machine has
a mechanical advantage (MA) of 10.
 In machines that increase distance instead of force,
the MA is the ratio of the output distance and input
distance.
 MA = output/input
Efficiency
 We said that the input force times the distance
equals the output force times distance, or:
Input Force x Distance = Output Force x Distance
However, some output force is lost due to
friction.
 The comparison of work input to work output is
called efficiency.
 No machine has 100 percent efficiency due to
friction.
Mechanical Advantage with Inclined Plane
Word Problems
1) Explain who is doing more work and why: a
bricklayer carrying bricks and placing them on
the wall of a building being constructed, or a
project supervisor observing and recording the
progress of the workers from an observation
booth.
2. How much work is done in pushing an object
7.0 m across a floor with a force of 50 N and
then pushing it back to its original position? How
much power is used if this work is done in 20
sec?
Word Problem Answers
Explain who is doing more work and why: a
bricklayer carrying bricks and placing them on
the wall of a building being constructed, or a
project supervisor observing and recording the
progress of the workers from an observation
booth. Work is defined as a force applied to an
object, moving that object a distance in the
direction of the applied force. The bricklayer is
doing more work.
2. How much work is done in pushing an object
7.0 m across a floor with a force of 50 N and
then pushing it back to its original position? How
much power is used if this work is done in 20
sec? Work = 7 m X 50 N X 2 = 700 N-m or J;
Power = 700 J /20 sec = 35 W
Work / Power Questions
1) Adrian and his friends find themselves out of gas on
the side of the highway. They apply a cumulative
force of 1080 N to push the car 218 m to the nearest
fuel station. Determine the work done on the car.
Work / Power Questions
2) Lamar Gant, U.S. powerlifting star, became the first
man to deadlift five times his own body weight in 1985.
Deadlifting involves raising a loaded barbell from the
floor to a position above the head with outstretched
arms. Determine the work done by Lamar in
deadlifting 300 kg to a height of 0.90 m above the
ground.
Work / Power Questions
3)During the Powerhouse lab, Jerome runs up the stairs,
elevating his 102 kg body a vertical distance of 2.29
meters in a time of 1.32 seconds at a constant speed.
Determine the power generated by Jerome.
Work / Power Questions
4) The Taipei 101 in Taiwan is a 1667-foot tall, 101-story
skyscraper. The skyscraper is the home of the world’s
fastest elevator. The elevators transport visitors from
the ground floor to the Observation Deck on the 89th
floor at speeds up to 16.8 m/s. Determine the power
delivered by the motor to lift the 10 passengers at this
speed. The combined mass of the passengers and
cabin is 1250 kg.
Mechanic Advantage Problems
5) Javon uses a wheelbarrow to lift a load of bricks. The
bricks weigh 600 N, which is more than Javon could
normally carry. However, with the wheelbarrow, Javon
can lift the bricks with as little as 120 N. What is the
mechanical advantage of the wheelbarrow?
Mechanical Advantage Problems
6) Jose wants to remove a tree stump from the ground.
To do this, he puts one end of a long beam under the
stump and puts all of his weight on the other end. His
weight is just enough to lift the stump. The stump
weighs 400 N. Jose weighs 250 N. What is the simple
machine Jose is using and the mechanical advantage of
that simple machine?
Types of Energy
 Potential energy, stored energy based on position.
 Kinetic energy, the energy of movement.
Potential Energy- Stored
 Gravitational potential energy is the energy
stored in an object as the result of its vertical
position or height.
 More massive objects have greater
gravitational potential energy.
 The higher that an object is elevated, the
greater the gravitational potential energy.
 PEgrav = mass • g • height
Another form of Potential Energy
 Elastic potential energy is the energy stored in
elastic materials as the result of their stretching or
compressing.
 The more stretch, the more stored energy.
Kinetic Energy- Motion
 There are many forms of kinetic energy -
vibrational (the energy due to vibrational
motion), rotational (the energy due to
rotational motion), and translational (the
energy due to motion from one location to
another).
 Our class will only focus on translational
energy.
 KE = 0.5 • m • v2
m = mass of object and v = speed of object
Word Problem Example
1. A cart is loaded with a brick
and pulled at constant speed
along an inclined plane to the
height of a seat-top. If the
mass of the loaded cart is 3.0
kg and the height of the seat
top is 0.45 meters, then what is
the potential energy of the
loaded cart at the height of the
seat-top?
Word Problem Ex. Answer
A cart is loaded with a brick and pulled at constant
speed along an inclined plane to the height of a seattop. If the mass of the loaded cart is 3.0 kg and the
height of the seat top is 0.45 meters, then what is the
potential energy of the loaded cart at the height of the
seat-top?
 PE = m*g*hPE = (3 kg ) * (9.8 m/s/s) * (0.45 m)
 PE = 13.2 J
Word Problem #2
 Determine the kinetic energy of a 625-kg roller coaster
car that is moving with a speed of 18.3 m/s.
KE = 0.5*m*v2
KE = (0.5) * (625 kg) * (18.3 m/s)2