Download Matter in Motion

MATTER IN MOTION
Vocabulary
• Motion: an objects change in position relative to a
reference point
• Speed: the distance traveled divided by the time interval
during which the motion occurred.
Speed practice
• Units for measuring speed: m/s, mph, km/s
• Finding your average speed
• Average speed = total distance/total time
• Example: If I traveled in my car for 4 hours and a distance of 360 kilometers,
what was my average speed?
• Let’s practice!
• What will we need to find the average speed a human walks?
Average Human’s Walking Speed
Students
Trial 1
Trial 2
Trial 3
Average
ft/sec
A
B
C
What is the average of all three walkers?
___________________
Vocabulary Continued
• Velocity: the speed of an object in a particular direction
• Example: A car was driving 35 mph, North.
• Resulting velocity: Combining more than one velocity.
• Example: a person walking backwards in a bus which is traveling
forward.
• The man is walking at 1 m/s backwards and the bus is traveling 15 m/s
forward, so the man’s resulting velocity is: ______________________
Acceleration
• Acceleration: the rate at which velocity changes over
time; an object accelerates if its speed, direction, or both
change
• Positive acceleration: an increase in velocity
• Negative acceleration: a decrease in velocity
Finding Acceleration
• Average acceleration =
• Final velocity – starting velocity
time it takes to change velocity
• Example: What is the average acceleration of a subway train that
speeds up from 9.6 m/s to 12 m/s in 0.8 s on a straight track?
• 3 m/s/s
WHAT IS FORCE?
Vocabulary
• Force:
• a push or a pull exerted on an object in order to change the motion
of the object; force has a size and direction.
• Newton (N):
• The SI Unit for force
• Net Force:
• The combination of all of the forces acting on an object
Understanding Net Force
More on Net Forces
Unseen Forces
• What are some unseen forces?
• Magnets
• Gravity
• Static Electricity
Balanced and Unbalanced Forces
• Balanced Force:
• When the forces on an object produce a net force of 0 N.
Unbalanced Force:
When the net force on an object is not 0 N. It produces a
change in motion
Friction and it’s affects
• Friction Defined:
• A force that opposes motion between two surfaces that are in
contact.
• Gently rub your hands together rapidly
• The harder you push the object increases the amount of friction
between the objects, which increases the heat
• The rougher the surface the more “hills and valleys” it has, also
increases friction
Types of Friction
• Kinetic Friction
• The word “kinetic” means moving. So, kinetic friction is the friction
between moving surfaces
• Static Friction
• The word “static” means not moving. So, when force is applied to
an object, (you try pushing on a heavy dresser) and it does not
move, that is static friction.
Usefulness of friction
• What are some good uses of friction?
• Brake pads on a car
• Rubbing sticks together to create a fire
• How can Friction be a bad thing?
• Car engines can over-heat, due to friction
• Solution: Lubrications, like engine oil
• Getting holes in your socks
• Solution: buy better socks…
Gravity
• Gravity defined:
• A force of attraction between objects that is due to their masses
• ALL matter has mass. Gravity is a result of mass. Therefore, all objects
in the universe have gravity. Which means all objects experience an
attraction to all other objects.
• The larger the mass of an object the more pull of gravity it has
• The Earth is the largest object to us, therefore we are pulled to it more
than any other object.
• Sir Isaac Newton “discovered” gravity and the Law of Universal
Gravitation was created in 1622
• It is universal, because it is true everywhere in the universe!
Imagine if…
• Tear out a separate sheet of paper and write this prompt
at the top of the page:
• Imagine if the Law of Universal Gravitation no longer existed…
• How would this change things?
• What would we need to do to change how we live?
• Think about how we would need to get food and water.
• Think about how our habitats would change.
• Etc.
Gravity and Motion
• Objects fall to the
ground at the same
rate, because the
acceleration is due to
gravity is the same for
all objects
• Remember:
Acceleration is the rate
at which velocity
changes.
Finding the Velocity of a Falling Object
•
v=gXt
• To find the change in velocity you need to
understand that g= the acceleration due to
gravity on Earth, or 9.8 m/s/s
• The “t” is how many seconds the object is
falling.
Practice finding the Velocity of a Falling Object
• If an object falls for 3 seconds, what is its velocity?
• 29.4 m/s
• What if an object falls for 10 seconds, what is its velocity?
• 98 m/s
Exceptions to the rule…
• Finding the velocity of an object on Earth would be easy, if
we lived in a vacuum.
• However, because we have wind resistance – friction, objects don’t
continually speed up, this is called:
• Terminal Velocity: the constant velocity of a falling object when the
force of air resistance is equal in magnitude and opposite in
direction to the force of gravity.
• Basically you are still falling, but you are no longer speeding up.
• Free Fall: the motion of a body when only the force of
gravity is acting on the body.
• If we lived in a vacuum we would not have wind resistance and would
continually speed up until we hit the ground.
• This means hail would travel at 11.2 km/s, or 25,000 mph
• A bullet travels at 1,700 mph
• When objects orbit larger objects, such as the International Space
Station orbiting the Earth, they are in Free Fall
• When objects are orbiting, they are continually falling, but they just
keep missing.
Projectile Motion
• Defined: the curved path that an object follows when
thrown, launched, or otherwise projected near the surface
of Earth.
Physics Math Practice…
• Resulting Velocity = combination of more than one velocity
• Unit: m/s and the direction the object is traveling.
• Average acceleration = Final velocity – starting velocity
time it takes to change velocity
• Unit: m/s/s
• Average speed = total distance/total time
• Unit: m/s, mph, km/h
• Net Force = if the two are going in the same direction it is
an addition problem, opposite direction it is a subtraction
problem
• Unit: N and the direction the object is traveling
•
v=gXt
Unit: m/s
Math Practice
• Find the resulting velocity if you are on a bus traveling
north at 12 m/s, you stand up and walk backwards at 3
m/s. What is your resulting velocity?
• 9 m/s north
• Find the Net force of an object, if one person is pull a box
to the right with 45 N of force. There is a second person
pulling the box in the other direction 23 N, What is the Net
Force?
• 22 N Right
• Find the average acceleration of a car the started out
traveling 15 m/s and ended up going 25 m/s, in a straight
line, and took them 5 seconds.
• 2 m/s/s
More Math!!!!
• Find the average speed a truck traveled if they were on
the road for 6 hours and traveled 240 miles.
• 40 mph
• Find the change in velocity of an object that fell to Earth
for 13 seconds, if it were in a vacuum
• 127.4 m/s
• Bonus Question: Solve the same problem if the object
were dropped on Venus… The rate of acceleration on
Venus is: 9.5 m/s/s. Also, solve for Jupiter, with its
acceleration being: 24.5 m/s/s. And finally the Sun, at:
275m/s/s
• Venus: 123.5 m/s Jupiter: 318.5 m/s Sun: 3,575 m/s
Newton’s Laws of Motion