PHYSICS
REVIEW
MR. BALDWIN
10/4/13
Aim: What have we done so far? Let’s review.
Do Now: Please take out your notebooks and
make a list of what we have done so far?
HOMEWORK:
Prepare for TEST on Monday 10/7/13.
A brief review sheet will be posted online.
1.
2.
3.
4.
5.
6.
7.
Rules of Significant figures.
Scientific and decimal notation
7 basic Units of measurement
Precision & Accuracy
Order of magnitude
Unit conversions between metric and BEU; between metric
Scalars and vectors
–
–
Definition & Components of vectors
Examples of both: Speed, distance, and time are scalar quantities;
Velocity, displacement and acceleration are all vectors.
8. Making line graphs
9. Constant and accelerated motion.
10. Freefall Motion
11. Distance & velocity-time graphs.
7 Basic Units of Measurement
In Physics, we
will be working in
the SI system,
where the basic
units are
kilograms, meters,
and seconds
(m.k.s).
METRIC PREFIXES
revised
These are the standard SI
prefixes for indicating
powers of 10.
CHECK
Can you give any
common everyday
examples where these
prefixes are used?
Section Check
Question
A car is moving at a speed of 90 km/h. What is the
speed of the car in m/s? (Hint: Use Dimensional
Analysis)
A. 2.5×101 m/s
B. 1.5×103 m/s
C. 2.5 m/s
D. 1.5×102 m/s
 90 km

 hr
  1000m   1hr


  1 km   60 min
  1min 

  25m / s
  60s 
Order of Magnitude: Rapid Estimating
A quick way to estimate a calculated quantity is
to round off all numbers to one significant figure
and then calculate. Your result should at least be
the right order of magnitude; this can be
expressed by rounding it off to the nearest power
of 10.
Section Check
Calculate approximately how many basketballs
(diameter = 75cm) can fit in this classroom randomly
AND orderly stacked one atop the other?
Accuracy & Precision
• Accuracy:
• Precision:
• How close you are to the
• How finely tuned your
actual value
• Depends on the person
measuring
• Calculated by the formula:
% Error = (YV – AV) x 100 ÷ AV
measurements are or
how close they can be
to each other
• Depends on the
measuring tool
• Determined by the
number of significant
digits
Where: YV is YOUR measured Value &
AV is the Accepted Value
Components of Vectors
If the components
are perpendicular,
they can be found
using
trigonometric
functions.
Addition of Vectors: Resultant
For vectors in same or
opposite direction, simple
addition or subtraction are
all that is needed.
You do need to be careful
about the signs, as the figure
indicates.
Recall
•
•
•
•
Graphs are made using pairs of numbers (x,y).
independent variables are plotted on the x-axis.
dependent variables are plotted on the y-axis.
Range is the difference between smallest and
largest value for a variable
• Scale determined by dividing the range by the
number of data points and rounding off to the
nearest integer.
• Titles must be give to graph &placed on both
axes
Uniform & Accelerated Motion
• Uniform motion refers to motion that has a
constant velocity
– Speed & direction remains the same
– Such as your car on cruise control
– Moving at 50 mph on a straight road
• Accelerated motion refers to motion with
changing velocity
– As you round a curb
– Hit the gas or brake
12
Average Speed & Instantaneous Speed
• The instantaneous speed is the speed as given on
your speedometer. The speed at that instant.
•Speed given by the speedometer
• The average speed is the total distance traveled
by an object divided by the total time taken to
travel that distance.
d
v
t
CHECK: Determine the units
Unit: m/s; km/h; mph
13
CHECK: Can you write other forms
of the equation to determine the other
two quantities t & d?
d
=
t
t=
d

d  v t
14
Acceleration
Acceleration is the change of velocity divided by time.
a
v f  vi
t
Where a: acceleration; vf: final velocity; vi:initial velocity
Determine its Unit.
Unit: m/s2
15
Equations of Motion
For Uniform (Constant) Motion, we use
d
d
v ; t
OR
t
v
d  v t
For Accelerated Motion, we use
v f  vi
v f  vi  at
OR a 
t
1 2
d  vi t  at
2
2
2
2
2
v f  vi  2ad
OR
v f  vi  2ad
16
Uniformly Accelerated Motion
Galileo’s Law of Freely
Falling Bodies:
In the absence of air
resistance, all objects,
regardless of size, shape
or mass, fall with the
same acceleration.
17
Finding Speed: What can you say about the slope of the
graph at any time?
The slope of the tangent to the distance-time graph at
any point is the instantaneous speed at that point.
25
20
8.00 m/s
15
10
4.00 m/s
5
0
0
1
2
3
4
5
18
Speed-Time Graph of Uniformly Accelerated Motion
v f  vi  at
Slope gives acceleration of the body at each point.
10.00
SPEED (m/s)
8.00
Slope 2.00 m/s2
6.00
4.00 m/s
4.00
2.00 s
2.00
0.00
0.00
1.00
2.00
3.00
TIME (s)
4.00
5.00
19
Graphical Analysis of Linear Motion
CHECK
How would you find the
area under the velocity-time
graph?
The area beneath the
velocity-time graph
gives you the Distance
travelled
20
TEST YOURSELF…WHAT DO YOU UNDERSTAND?
SCIENTIFIC & DECIMAL NOTATION
How do you write a decimal in scientific notation?
What is the form?
METRIC PREFIXES
What are the metric prefixes?
What values do the symbols represent?
MOTION
What is motion?
How do you measure motion?
SCALARS & VECTORS
What is a Scalar?
What is a Vector?
Give some examples of both scalar and vector quantities.
VELOCITY
What is Velocity?
What is the formula for Velocity?
What is the Unit?
Is it a Scalar or Vector?
ACCELERATION
What is Acceleration?
What is the formula for acceleration?
What is the unit for acceleration?
PHYSICS
NEWTON’S LAWS
MR. BALDWIN
10/8/13
Aim: Would a hockey puck sliding on a
frictionless ice ever stop?
Do Now: What forces are acting on you as
you sit in your seat?
Homework: “Motion is the rule, not the
exception.” Think about this statement.
Find some interesting quotes on your
own by Isaac Newton.
Newton’s First Law
The Law of Inertia
Laws of Motion: Questions for Thought
• What makes something originally at rest
begin to move?
• Why do some things move faster than
others?
• Why are some objects accelerated and
others not?
Question: What Causes an Acceleration?
• If a body changes in its state of rest or uniform
motion, then it underwent an acceleration.
• What caused this?
– A force
– Simply described as a push or pull on and object.
• Thus, a net unbalanced force changes the object’s
state of inertia
– i.e. state of rest or uniform (constant) motion
• A net unbalanced force causes an acceleration
• NOTE: A force is not a characteristic of an object. “It
is something that one object does to another.”
CHECK: What are some examples of force?
Contact Forces
Action-at-a-Distance Forces
Frictional Force
Gravitational Force
Tension Force
Electrical Force
Normal Force
Magnetic Force
Air Resistance Force
Applied Force
Spring Force
Newton’s First Law of Motion
• Constant velocity is as natural as being at rest.
• If you give a ball a push on a frictionless floor,
it would move forever.
• This conclusion was first reached by Galileo
and later stated by Newton as his first law of
motion.
Newton’s First Law of Motion
Newton’s first law is often called the
law of inertia.
Every object continues in its state of rest,
or of uniform motion in a straight line,
unless acted upon by an unbalanced
(external) force.
Examples of Inertia
Newton’s First Law of Motion states:
If no net unbalanced force acts on
it, an object at rest remains at rest
and an object in motion remains in
motion at a constant velocity (that is
at constant speed in a straight line).
END. Test your skills
• http://phet.colorado.edu/sims/lunarlander/lunar-lander_en.html
PHYSICS
NEWTON’S 2nd LAW
MR. BALDWIN
10/15/13
Aim: Why are some objects accelerated
faster then others?
Do Now: Is it ever possible for a steel rod
and a handful of feathers to have the
same mass? Explain.
Homework: Worksheet : Newton’s 2nd Law
Do Problems 6 - 10
What is Inertia?
Inertia is the tendency of an object to
resist any change in its state of rest or
uniform motion.
What is Mass?
 The mass of a body is the property of
matter that manifests itself as inertia.
 In other words, mass is a measure of
inertia.
Mass
• Mass may be thought of as a quantity
of matter contained in an object.
– Matter is anything that occupies space
• The greater an object's mass, the
greater the object's inertia.
• The SI unit for mass is the kilogram
(kg).
Force CHECK.
• According to the first law, can an object
begins to move all by itself?
• No! A force is needed to start it moving.
• If an object is moving in a straight line,
will it continue to move in a straight line
at a constant velocity?
• Yes! Unless a force acts to slow it down,
speed it up, or changes its direction.
Therefore, what can you conclude
about a force?
• A force is any influence that can
change the speed or direction of
motion of an object.
• A force is any influence that can
cause an object to be accelerated.
What variables determine whether
an object accelerates?
• If you push the same chair with two different
forces (one small & one large), describe its
motion?
• What can you conclude about your choice?
• If you push a chair and a table with the same
force, which one accelerates faster?
• What can account for your choice?
Newton’s Second Law of Motion
Newton’s second law is the relation between
acceleration and force. It states, the acceleration
of an object is proportional to force and
inversely proportional to its mass.
Force is a vector
• Force is a vector, so
Fnet  m  a .
• NOTE: The direction of the
acceleration is always in the same
direction as the force.
Now, Derive the base units of force
from the equation.
The Newton: The Unit of Force
The unit of force in the
SI system is the Newton.
Unit: 1 N = 1 kg·m/s2
Note that the pound is a
unit of force, not of
mass.
The Newton: the unit of force
F  ma
• The SI unit of force is the Newton (N)
• 1 Newton = 1 N = 1 (kg)(m/s2)
• The pound (lb) is the unit of force in the
British system of measurement
• 1 lb = 4.45 N (1 N = 0.225 lb)
A force of 1 Newton gives a mass of
1 kilogram an acceleration of 1 m/s2
Force
The magnitude of a force can be
measured using a spring scale.
Worksheet: DO problems 1 – 5
DEFINITIONS
• Collinear Forces:
forces whose
vectors lie along
the same straight
line.
• Concurrent
Forces: Forces
whose line of
action pass through
a common point.
F3
F3
F1
F2
F1
F2
PHYSICS
NEWTON’S 3rd LAW
MR. BALDWIN
10/17/13
Aim: What is the difference between mass
and weight?
Do Now: QUIZ (8 min)
Take out your Newton’s 2nd law
worksheet and do #11 on a sheet of
paper & turn in.
Homework:
Effect of Force on Mass: Complete
the following statement
• When forces of different magnitudes act
upon different objects of identical masses,
the greater force produces the
greater/lesser acceleration.
• When the same force acts on objects of
different masses, the greater mass receives
the greater/smaller acceleration.
Friction: just another force
• Friction is a force that acts to oppose the
motion of an object with which it is in
contact.
– The harder the objects are pressed
together, the stronger the frictional
force.
– Friction is an actual force, unlike
inertia.
??? Question for Thought ???
• An astronaut has a mass of 80 kg on earth.
What will his mass be on the Moon? Calculate
or Explain.
• Describe what would happen to the spring in a
bathroom scale if you were on the moon when
you stepped on it. How is this different from
stepping on the scale on Earth?
• http://phet.colorado.edu/sims/mass-springlab/mass-spring-lab_en.html
Weight – the Force of Gravity
Weight is the force exerted on an object
by gravity. Close to the surface of the
Earth, where the gravitational force is
nearly constant, the weight is:
w  mg
The Newton: the unit of force
• Weight is a Force. SI unit of weight is the
Newton (N)
• The pound (lb) is the unit of force in the
British system of measurement
• 1 lb ≈ 4.45 N OR (1 N = 0.225 lb)
• Mass/Weight equivalence:1 kg ≈ 2.2 lbs.
CHECK.
What is your mass in Kilograms?
1kg
180 lbs 
 82 kg
2.2lbs
CHECK.
What is your weight in Newtons?
Mass, m  80.0kg
Weight, w  mg

w   80.0kg  9.80m / s
2

 780kg  m / s  780 N
2
Convert your weight from Pounds to
Newtons?
Weight, w  180lbs
1lbs  4.45 N
4.45 N
Therefore, 180lbs  180lbs 
 800 N
1lb
What is the weight, in Newtons, of a
1200 kg automobile?
Mass, m  1200kg
Weight, w  mg

w  1200kg  9.80m / s
2

 11760kg  m / s  11.76kN
2
Weightlessness
• Are you ever weightless?
–w=0
• Weightlessness is just a sensation
• Have you ever experienced weightlessness?
PHYSICS
MR. BALDWIN
NEWTON’S 3rd LAW
10/18/13
Aim: What is Newton’s 3rd law?
Do Now: REAL QUIZ (8 min)
A rocket accelerates in a space at a rate of 1-g.
The rocket exerts a force of 2482 N. (i) What
is the mass of the rocket? (ii) Later in flight,
the rocket exerts a force of 46,458 N. What is
the rocket’s new acceleration? What is the
rocket’s new acceleration in g’s?
Homework:
Newton’s Third Law of Motion
Law of Force Pairs:
All forces occur in pairs
For every action force
there is an equal and
opposite reaction force.”
Newton’s Third Law of Motion
Any time a force is exerted on an object, that force is
caused by another object.
Newton’s third law: law of force pairs
Whenever one object exerts a force on a second object, the
second exerts an equal force in the opposite direction on
the first.
Newton’s Third Law of Motion
A key to the correct
application of the
third law is that the
forces are exerted on
different objects. Make
sure you don’t use
them as if they were
acting on the same
object.
Newton’s Third Law of Motion
Rocket propulsion can also be explained using Newton’s
third law: hot gases from combustion spew out of the
tail of the rocket at high speeds. The reaction force is
what propels the rocket.
Note that the rocket
does not need
anything to “push”
against.
WHAT ARE the reaction forces?
• Action: the tires on a car push on the road…
• Reaction: the road pushes on the tires.
• Action: while swimming, you push the water
backwards...
• Reaction: the water pushes you forward.
• Action: a rocket pushes out exhaust…
• Reaction: the exhaust pushes the rocket
forward
You come up with other examples
of action-reaction forces?