Download Motion Notes

Page 41
Motion
What is motion and how can I determine if motion
has occurred? What is the difference between
distance and displacement?
Motion is the change in position or condition of an
object.
A point of reference is an object that appears to
remain at rest in relation to an object that is in motion.
Examples – building, street, traffic signal.
There are two types of quantities that are used to
describe motion: vector and scalar. Vectors are
quantities that are described by both a magnitude and
a direction. Scalars are quantities described only by a
magnitude.
On page 40 of your INB, make two columns and categorize the following
descriptions as scalar or vector:
3 feet
2 miles
43 miles west
27 inches north
78 meters northwest
Scalar
187 meters east
16 feet
1 foot
Vector
Page 43
Distance is how much ground an object has covered during its
motion (for example 20 meters)
Displacement is how far out of place an object is, or the
object’s change in position (for example, 8 meters south east)
10m
5m
START
15m
8m
20m
END
On top half of page of your INB, write the directions from this class to the cafeteria
.
On bottom half of page of your INB, write the directions from your home to school
using appropriate points of reference:
Page 45
Speed is the rate that an object moves. (How fast something
moves). It is scalar quantity.
Speed is measured in meters per second (m/s), kilometers per
hour (km/hr) and miles per hour (mph)
There are two types of speed: instantaneous and average.
Instantaneous speed is the speed in that particular moment (in
a car)
Average speed is the speed of a total distance divided by the
total time it takes to travel the distance.
Average speed is calculated using the formula:
Speed = distance traveled
time of travel
Page 47
Velocity is the rate that an object changes its position. It is a
vector quantity.
Velocity is measured in meters per second (m/s), Kilometers
per hour (km/hr) and miles per hour (mph) with a direction.
For example:
40 m/s west
Velocity is useful for airplanes, helicopters and boats.
Velocity is calculated by dividing the amount of displacement
by the time it takes to travel the distance.
Velocity = displacement / time of travel
SPEED AND VELOCITY ARE NOT THE SAME
On page of your INB, make two columns and categorize the following descriptions
as speed or velocity:
car moving at 35mph
bird flying at 40mph north
jogger running at 10m/s
jogger running at 10m/s south
a vehicle racing at 125mph
Speed
Velocity
Page
S8P3a.
Motion
What is the relationship between velocity and acceleration?
Acceleration is the rate at which an object’s velocity
changes.
There are 3 ways that acceleration can occur:
1. speeding up (acceleration or positive acceleration)
2. slowing down (deceleration or negative
acceleration)
3. Changing direction
Acceleration is expressed in units like meters per
second squared (m/s2)
The formula for calculating acceleration is:
Average acceleration= final velocity-initial velocity
time
Summary
On the top half of pg. of your Science NoteBook
Identify which is an example of acceleration and which is not:
Acceleration
Not Acceleration
A train traveling 65 miles per hour north
A boat sailing west at 5 knots
A person jogging at 3 meters/second along a curved path
A car stopped at a stop light
A car stopping at a stop light
A truck speeding up from 55mph to 75mph
A person jogging at a constant speed along a straight path
Page
S8P3a.
Graphing Motion
How can motion be visually represented through graphs?
Graphing is a way to represent the motion of objects. They are useful to see
trends, understand past movements and to predict future movements.
When plotting motion, time is always plotted on the X-axis (bottom of the graph).
The further to the right on the axis, the longer the time from the start. Distance or
speed (depending on the graph) is plotted on the Y-axis (side of the graph).
Page 51
Graphing is a way to represent the motion of objects. They are useful to
see trends, understand past movements and to predict future movements.
When plotting motion, time is always plotted on the X-axis (bottom of the
graph). The further to the right on the axis, the longer the time from the
start. Distance or speed (depending on the graph) is plotted on the Y-axis
(side of the graph).
For Distance-Time Graphs:
•The steeper the graph, the faster the motion.
•A horizontal line means the object is not moving. It is stationary..
•A curved line means the speed is changing by speeding up or slowing
down.
A steeper line indicates a larger
distance moved in a given time. In
other words, higher speed.
Both lines are straight, so both
speeds are
constant.
Time is increasing to the
right, but its
distance does not change. It
is not
moving. We say it is At Rest.
The line on this graph is
curving upwards. This
shows an increase in
speed, since the line is
getting steeper:
Page
For Speed-Time Graphs:
•The steeper the graph, the greater the
acceleration.
•A horizontal line means the object is moving at
a constant speed
•A downward (negative) sloping line means the
object is slowing down (decelerating).
Both the dashed and
solid line show
increasing speed.
Both lines reach the
same top speed, but
the solid one takes
longer.
The dashed line
shows a greater
acceleration.
A straight
horizontal line on
a speed-time
graph means that
speed is constant.
It is not changing
over time.
A straight line
does not mean
that the object is
not moving!
This graph shows
decreasing speed.
The moving
object is
decelerating.
Page 49
A force is a push or pull on an object. There are many
different types of forces in nature that act on objects.
They include: gravity, friction and inertia.
Gravity is an attractive force that works to pull objects
together.
The law of universal gravitation states that a force
of gravity acts between all objects in the universe.
There are two factors that affect the force of gravity
between objects: 1. the objects’ masses (mass is the
amount of matter in an object). and 2. the distance
between them.
Page 49
The larger the mass, the more the gravitational
attraction. For example, the sun has a greater ability
to “pull” objects towards it than Mars because of its
mass.
The shorter the distance between the objects, the
more the gravitational attraction. The Earth and Mars
have more attraction than the Earth and Venus.
Inertia is the tendency of an object to resist a change
in motion.
Mass affects inertia. An object with a large mass
has more inertia than an object with a small mass.
On page
Draw/write the following 3 questions and determine which has a greater
gravitational “pull” and WHY.
1.
25kg
3.
25kg
25kg
35kg
25kg
2.
25kg
Set A (red)
25kg
Set B (green)
5kg
The force that brings nearly everything to a stop is called friction.
Page 51
Friction is the force that opposes the motion of an object. This contact force
acts whenever an object in motion rubs against a surface. Friction opposes
motion when two surfaces touch. The contact reduces the speed of the
moving object and releases heat.
There are 3 types of friction: sliding friction, rolling friction and static friction
Sliding friction is friction that slows down an object that slides. Example:
brake pads on a bicycle that rub against the wheel
Static friction is friction that acts on an object at rest. Example: trying to
move a refrigerator
Rolling friction is friction that acts when an object rolls across a surface.
Example: rolling a cart around
All motion is due to forces acting on objects. Force is a vector
quantity and is measured in a unit called Newtons (N).
Page 53
The net force is a total combination (sum) of all forces acting on an
object.
A balanced force is one in which the net forces equal zero. The
motion does not change.
An unbalanced force has a net force greater than zero. Only an
unbalanced force can change the motion of an object.
An unbalanced force acting on an object at rest will cause it to
move.
Page 53
An unbalanced force that acts on an object already in motion can
change the speed OR direction of an object.
Unbalanced forces can act in the same direction or in opposite
directions. If forces are in the same direction, you add them. If forces
are acting in the opposite direction, you subtract them.
5N
3N
Net force = 8N east
5N
5N
9N
Net force = 4N west
5N
Net force = 0N
On page 50
Draw an illustration of friction in action. Your
illustration must be neat and colored. You
must identify the two surfaces that are
interacting and what is occurring in order for
it to be friction. You must also identify the
type of friction.
On pg.52 of your Science INB
Draw the figures below and calculate the net force.
Remember to include the direction of motion.
6N
4N
1N
9N
10N
2N
6N
4N
2N
5N
5N
8N
8N
7N
9N
5N
5N
9N
5N
5N
5N
5N
1N
4N
5N
Question 1
• What happens to the motion of an object
when the forces are balanced?
– A. The motion changes.
– B. The motion does not change.
– C. The motion speeds up.
– D. The motion slows down.
On pg.78 of your Science INB
During the game of tug-of-war
What happens when the two teams pull with equal force?
What type of forces are these called?
How would you represent this with force arrows?
Illustrate and color.
What happens when one team pulls with a greater force?
What type of forces are these called?
How would you represent this with force arrows?
Illustrate and color.
Make an Inference:
What would have happened if the game has been played
on ice?
Question 2
• What happens to an object if the forces acting
upon it are unbalanced?
– A. Its motion will not change.
– B. The motion will come to a stop.
– C. The net force will be zero.
– D. Its motion will change.
Top of
page 82
Earth
Moon
Actual Orbit
Gravity and inertia work together to keep the Moon orbiting Earth. First, the
Moon’s inertia pushes it to travel continuously in a straight line. At the same
time, Earth’s gravity is pulling the Moon toward Earth. These combined forces
cause the Moon to move in a curved path (orbit) around Earth. Without gravity,
the Moon would fly off into space. The Moon is able to continuously orbit Earth
because the Moon’s inertia and the Earth’s gravity are balanced.
Question 3
• What happens to an object moving in the
same direction as the net force?
– A. It will speed up.
– B. Its motion will not change.
– C. It will stop moving.
– D. It will slow down.
Question 4
• Which pair of objects will have the greatest
gravitational attraction to each other?
– A. two cinder blocks 6 centimeters apart
– B. two marbles 12 centimeters apart
– C. a cinder block and marble 6 centimeters apart
– D. a cinder block and marble 12 centimeters apart
Page 5
S8P3b.
Laws of Motion
Since gravity works to pull objects toward each other, what
keeps the planets from crashing into the Sun?
Newton’s first law of motion states that an object at
rest will stay at rest, and an object in motion will
continue in motion in a straight line at the same speed
(same velocity) unless an unbalanced force acts on
the object.
This law is sometimes called the Law of Inertia.
This means if the net force acting on an object is zero,
the object remains at rest, or if the object is already
moving, continues to move in a straight line with
constant speed.
Page 7
S8P3b.
Newton’s laws
What is the relationship between force, mass and acceleration?
Newton’s second law of motion states that the acceleration of
an object depends on the mass of the object and the amount of
force applied.
Example: It takes more force to accelerate a full grocery cart than
an empty grocery cart.
OR
To use the same magnitude of force, you could take the groceries
out of the full cart (decrease the mass) to make the masses
equal.
This law can be expressed mathematically with:
Force = mass x acceleration
(newton) = (kilogram) x (meters/second2)
The acceleration of a falling object is 9.8m/s2
Top of page 6 – 1st period
How much force is needed to accelerate a 2 kilogramobject at a rate of 2 m/s2?
What is the mass of an object that requires a force of
30N to accelerate at a rate of 5 m/s2?
Calculate the acceleration of a 6.4kg bowling ball if a
force of 12N is applied to it.
page 8
How much force is needed to accelerate an 8 kilogramobject at a rate of 2 m/s2?
Top of page 6 3rd, 4th and 5th periods
How much force is needed to accelerate an 8 kilogramobject at a rate of 2 m/s2?
Top of page 6 3rd, 4th and 5th periods
How much force is needed to accelerate an 8 kilogramobject at a rate of 2 m/s2?
What is the mass of an object that requires a force of
30N to accelerate at a rate of 5 m/s2?
Top of page 8
How much force is needed to accelerate an 8 kilogramobject at a rate of 2 m/s2?
What is the mass of an object that requires a force of
30N to accelerate at a rate of 5 m/s2?
Calculate the acceleration of a 6.4kg bowling ball if a
force of 12N is applied to it.
Top of page 6
6th period
Newton’s Second Law & Air Resistance
• Air Resistance
• The force of air exerted on a falling object
• Fluid Friction
• The air pushes up as gravity pulls down
• Depends on shape, size, and surface area of the
falling object
• Terminal Velocity
• The highest velocity a falling object will reach
• An object reaches its terminal velocity when the
force of air resistance = the force of gravity
Bottom of page 6
Write the question and answer:
Name two ways to increase the acceleration of an
object.
1.
2.
What force is necessary to accelerate a 1,250kg
car at a rate of 40m/s2?
Page 9
When a person pushes on a wall, the wall pushes back.
How does this relate to Newton’s 3rd law?
Newton’s third law of motion states that for
every action there is an opposite and equal
reaction. Forces act in equal and opposite
pairs.
Example: pushing on a wall, a rocket
launching, diving off the side of a pool.
• A bowling ball hits the pins sending the pins flying for
a STRIKE!
• In a plane taking off you feel pushed back into your
seat (1st Law or 3rd Law)
• An object at rest stays at rest unless acted on by an
outside force
• An object in motion stays in motion unless acted on
by an outside force
• Seatbelt stops you from hitting the windshield if you
hit the brakes quickly
• A soccer ball will not move until a player kicks it
• Someone crashes their bike into a rock & is thrown
over it to the ground
• 12 lb bowling ball goes faster down the lane than a
15 lb bowling ball
• A boy can throw a football farther than his friend
because he uses more force
• Force = mass times acceleration
• It takes less force to move a DVD than a DVD player
• It takes less force to push a bike than a motorcycle
• More force = more acceleration
• Push a large box & a small box with the same force,
the small box will go faster
• You have to push a heavy ball harder to get it to
move as fast as a small one
• Feet push down on the floor & the floor pushes up at
feet as you walk
• A fireman turns on his hose & is knocked backwards
• For every action there is an = and opposite reaction
• If air is let out of a balloon quickly, air pushes down &
balloon goes up
• In a plane taking off you feel pushed back into your
seat (1st Law or 3rd Law)
• When you push on a door it pushes back with = and
opposite force
Page 11
S8P3c.
What is work?
Work is the transfer of energy to an object. In science, work is
done when a force causes an object to move in the direction
of the force. Applying forces does not always result in work.
Work requires two things:
•a force applied to an object
•the object must move in the direction of the force.
Example of work: pushing a lawnmower
Example of NO WORK: carrying a bag of groceries to the car.
The equation for work is:
Work = Force x Distance
(Joule) = (Newton) x (Meters)
The unit for work is the Joule (J). 1 Newton Meter = 1 Joule
Page 13
What is Power?
Power is the rate at which energy is transferred to
an object. (The rate that work is done.)
Power can be calculated using the formula
Power = Work
(Watt)=(Joule)
time
second
The unit of measure for Power is the Watt (W).
1 Watt = 1Joule/second
Practice Question:
A set of pulleys is used to lift a piano weighing 1,000
newtons. The piano is lifted 3 meters in 60 seconds.
How much power is used?
Page 10
A book with a force of 1.0 Newtons is lifted 2
meters. How much work was done?
A force of 15 Newtons is used to push a box along
the floor a distance of 3 meters. How much work
was done?
It took 500 Newtons of force to push a car 4
meters. How much work was done?
Page 15
S8P3c.
What are simple machines and how do they make work easier?
A simple machine is a device that makes work easier by 1.
changing the size of a force OR 2. changing the direction of a
force.
The six simple machines are:
Pulley, Inclined plane, Wedge, Wheel and Axle, Screw, and
Lever
•When you use a machine, you do work (work input) on the
machine and the machine does the work (work output) on
something else. The “work output” can never be more than the
“work input”. It will always be the equal.
•The input force may be less than the output force.
Page 90
An inclined plane is a straight, slanted surface.
They make work easier because it is easier to push
an object up a ramp than to lift the same object
straight up to the same height. Ex. a ramp
Page 90
A wedge is an inclined plane that is wider or thicker
at one end than at the other. A wedge makes work
easier because when moved, a wedge is used to
cut, split, or pry apart objects. Ex. knife blade or
axe.
Page 90
A screw is an inclined plane that is wrapped around
a cylinder. When a screw is turned, a small force is
applied over the long distance of the screw’s
threads.
Page 91
A lever is a simple machine that consists of a bar
that pivots at a fixed point called a fulcrum. The
force applied to a lever is called the effort. The
object being moved is called a load. There are
three classes of levers: 1st class, 2nd class and 3rd
class.
Page 92
A wheel and axle is a simple machine that consists
of a shaft called the axle, inside the middle of a
wheel. Ex. bicycle wheel
Any force that is applied to the wheel gets
transferred to the axle and vice versa. When force
is applied to the wheel, the difference in size
between the wheel and axle causes the force to
increase as it is transferred to the axle.
page 93
A pulley is a rope or chain wrapped around a
wheel. A load is attached to one end of the rope. A
force is applied to the other end of the rope.
There are 2 kinds of pulleys: fixed and movable.
A fixed pulley is one that does not move. They are
often used to lift something. A fixed pulley changes
the direction of force, but does not reduce the
amount of force needed to lift the load.
On page 17
Mechanical advantage is the number of times the
input force is multiplied by a machine.
Mechanical advantage = output force (Newtons)
input force (Newtons)
Efficiency is a measure of how well a machine
does work.
Efficiency = output work (joules)
X 100%
input work (joules)
On pages 94
A man expends 100 Joules of work to move a box
up an inclined plane. The amount of work produced
is 80 Joules. What is the efficiency?
A box with a force of 100 Newtons is pushed up an
inclined plane that is 5 meters long. It takes a force
of 75 Newtons to push it to the top, which has a
height of 3 meters. What is the efficiency of the
machine.
MOMENTUM
On page 94
Momentum = mass x velocity
A 10,000kg train is traveling east at 15 m/s.
Calculate the momentum of the train.
What is the momentum of a car with a mass of
900kg traveling north at 27m/s
Page
A movable pulley is a pulley that moves. One end
of the rope is tied to a stationary object and the
other is free for you to pull on. The load is attached
directly to the pulley. The pulley moves along the
rope as the free end is pulled. They reduce the
amount of force needed to move an object, but you
must pull the rope farther.
page
A block and tackle is a system (combination) of
pulleys.