gravity and friction ppt

mechanics

1. Agenda
•FF
•EQ
•Notes on Friction & Gravity
•I Bet You Can’t Activity
•Present HW
•Closure

2. 2 Volunteers
•Socks vs. Shoe Friction Demontration

3. Questions
•does it make a difference sliding in socks?
explain.
•
•Is it easier or harder on carpet than wood
or tiles?
•
•how do you think friction affects motion
based on what you observed?

4. FRICTION AND GRAVITY
NOTES
•Performance Indicator
•8.P.2A.5Analyze and interpret data to
describe and predict the effects of forces
(including gravitational and friction) on the
speed and direction of an object.
•

5. What is a force?
•A force is a push or pull

6. Types of Forces
•1. Gravity
•2. Friction
•Forces such as gravity and friction can
affect the speed and direction of an
object.
•

7. Family Guy Video
•What is gravity?
•
•Why is gravity considered a
force?

8. Gravity (force that pulls objects down)
•Gravityis a force that always attracts or pulls
objects toward each other without direct contact
or impact.
•Gravity is a force of attraction, or a pull,
between objects.
•Gravity pulls objects down.
•Do gravity affects everything? ____________

9. What Position Does Gravity
Affect?
1
2
3
All

10. •Gravitational attractiondepends on the
massof the two objects and the distance
they are apart.
•Objects on Earth are pulled toward the
centerof Earth.

11. •The force of gravity, like all other forces,
can cause changes in the speed of objects.
•As an object falls, its speed will
continuallyincreaseas Earth’sgravity
continually pulls it downward. When air
resistance is ignored, all objects will speed
up at the same rate as they fall.

12. •Gravity can also cause an object that is
thrown into the air to change its upward
motion, slowdown, and fall back toward
Earth’s surface.
•The pull of Earth’s gravity keeps the
Moon in orbit; the moon is constantly
changing direction because of gravity.

14. How Does Mass Affect Gravity?
•Imagine an elephant and a cat. Because the elephant
has a larger mass than the cat does, gravity between the
elephant and Earth is larger. So, the cat is much easier
to pick up than the elephant. The gravitational force
between objects depends on the masses of the objects.
•Objects with Larger or Heavier Mass has a larger
gravitational attraction?
•Objects with a smallermass has a smaller
gravitational attraction.

15. How Does Distance Affect Gravity?
•The mass of the sun is 300,000 times bigger than that of Earth.
However, if you jump up, you return to Earth every time you
jump rather than flying toward the sun. If the sun has more mass,
then why doesn’t it have a larger gravitational pull on you?
•This is because the gravitational force also depends on the
distance between the objects.
•As the distance between two objects gets larger or further, the
force of gravity gets much smaller.
•And as the distance between objects gets smaller or shorter, the
force of gravity gets much greater.
•Although the sun has tremendous mass, it is also very far away. This means
that it has very little gravitational force on your body or on small objects
around you. The sun does have a large gravitational force on planets because
the masses of planets are very large.

16. Air Resistance
•When air resistanceis ignored, all objects
will speed up at the samerate as they fall.
•What is air resistance? Air resistance
opposes the downward motion of a falling
object.
•Any falling object meetsair resistance.

17. Questions
•WHAT TWO THINGS DETERMINE
GRAVITATIONAL FORCE?
•
•do all objects have a gravitational
force? explain your answer.
•

18. Questions
•IS THERE MORE GRAVITATIONAL FORCE
BETWEEN OBJECTS WITH SMALL MASSES OR
OBJECTS WITH LARGE MASSES?
•
•THE SUN IS MUCH MORE MASSIVE THAN
EARTH. WHY IS THE FORCE OF GRAVITY
BETWEEN YOU AND THE SUN SO MUCH LESS
THAN EARTH’S GRAVITY AND YOU?
•
•HOW DOES AIR RESISTANCE AFFECT AN
OBJECT’S MOTION?
•

19. Friction
•Frictionis a force that occurs when one
object rubsagainst another object.
•Friction will cause a moving object to
slow down and finally stop.
•Friction is the Force that one surface exerts
on another surface when they are moving
across each other.

20. •Two factors determine the amount of
friction –
•(1) the kinds of surfaces, and
•(2) the force pressing the surfaces
together. (how hard the surfaces are pushed
together during the motion )
•Friction can effect the speed and direction
of an object.

21. •Friction is the force that acts to resist sliding
between two surfaces that are touching. It
can slow down or stopthe motion of an
object.
•
•The slowing force of friction always acts in
the direction oppositeto the force causing
the motion.

22. –The slowing force of frictionalways acts in
the direction oppositeto the force causing the
motion.
–Friction Opposes motion
•Examples: rubbing hands together, gym
sneakers allowing you to stop better on the
gym floor (compared to dress shoes)

23. •For example, friction slows or stops the
motion of moving parts of machines.
•Another example would be athletic shoes
with tread grooves to increase friction have
better traction for starting or stopping
motion than smooth-soled dress shoes.
•

24. •Friction can also be the force that makes
it difficult to startan object moving.
•Enough forcemust be applied to a
nonmoving object to overcome the
frictionbetween the touching surfaces.

25. •The smootherthe two surfaces are, the less
friction there is between them; therefore,
the moving object will not slow down as
quickly.

26. –Friction between surfaces can be reduced, in
order for objects to move more easily, by
smoothing the surfaces, using wheels or
rollers between the surfaces, or
lubricating/oiling the surfaces.
–If friction could be removed, an object would
continue to move.

27. •The greater the force pushingthe two
surfaces together, the strongerfriction
prevents the surfaces from moving.
–As an object gets heavier, the force of friction
between the surfaces becomes greater.
–To move a heavy object, a greaterforce must
be applied to overcomethe frictionbetween
the surfaces.

28. Less or More Friction

29. Less or More

30. Less or More

31. Less or More

32. Types of Friction
•Static friction: the frictional force that
opposes any attempt to move a stationary
object along a surface.

33. •Sliding friction: (sometimes called
"kinetic" friction): this frictional force
opposes the sliding motion of two surfaces
rubbing together.

34. •Rolling frictionis a special case of static
friction.

35. •Fluid Frictionis the movement of solid
objects through a fluid ex: oil, water
and air.

36. Comparing Gravity and Friction

37. Center of Gravity Lab
•“BET YOU CAN’T BALANCE”CHALLENGES*
•Use what you've learned about balance to compete
with your friends and family with following balance
challenges.
•HERE WE GO!!!!!!
•http://nanaimoscience.org/wp-
content/uploads/2014/04/Playground-
Physics1.pdf