cot 1.ppt...FORCE AND MOTION,,BALANCE AND UNBALANCED

my first COT

2. Always Remember !Always Remember !

3. 
Objectives:Objectives:
1.Describe what fault is and how these faults
related to earthquakes.
Determine the extent of damage an
earthquake can do in a particular location

4. Introductory Activity: Introductory Activity:
Question:
It was mentioned in Grade 7 that the Philippines
is located along the Ring of Fire, How does this
affect us?

5. Read and analyze the statement:Read and analyze the statement:
On July. 1990, a strong earthquake hit On July. 1990, a strong earthquake hit
Luzon. Have you heard about it? Maybe not, Luzon. Have you heard about it? Maybe not,
because it happened before you were born. because it happened before you were born.
But if your parents are from Luzon, theyBut if your parents are from Luzon, they
surely know about the earthquake. It is surely know about the earthquake. It is
possible that they were even affected by it.possible that they were even affected by it.

8. Motion & ForcesMotion & Forces
Defining ForceDefining Force

ForceForce

Newton’s First LawNewton’s First Law

FrictionFriction

9. ForceForce

ForceForce

a a pushpush or or pullpull that one body exerts on another that one body exerts on another

What forces are being What forces are being
exerted on the football?exerted on the football?
F
kick
F
grav

10. ForceForce

Sometimes it is obvious that a Sometimes it is obvious that a forceforce has has
been applied. been applied.

But other forces aren't as noticeable.But other forces aren't as noticeable.

A force can cause the A force can cause the motionmotion of an object of an object
to to changechange..

If you have played billiards, you know that If you have played billiards, you know that
you can force a ball at rest to roll into a you can force a ball at rest to roll into a
pocket by striking it with another ball.pocket by striking it with another ball.

11. Changing MotionChanging Motion

The The forceforce of the moving ball causes the of the moving ball causes the
ball at rest to move in the ball at rest to move in the directiondirection of of
the force.the force.

Force does Force does notnot always change velocity. always change velocity.

12. ForceForce

Net ForceNet Force

unbalancedunbalanced forces that are not forces that are not
opposite and equalopposite and equal

velocityvelocity changes (object accelerates) changes (object accelerates)
F
friction
W
F
pull
F
net
NN

13. Balanced ForcesBalanced Forces

When two or more forces act on an When two or more forces act on an
object at the same time, the forces object at the same time, the forces
combine to form the combine to form the net forcenet force

The net force on the box is zero because The net force on the box is zero because
the two forces cancel each other.the two forces cancel each other.

Forces on an object that are equal in size Forces on an object that are equal in size
and opposite in direction are called and opposite in direction are called
balanced forcesbalanced forces. .

14. ForceForce

Balanced ForcesBalanced Forces

forces acting on forces acting on
an object that an object that
are are oppositeopposite in in
direction and direction and
equalequal in size in size

no change in no change in
velocityvelocity

15. Unbalanced ForcesUnbalanced Forces

When two students are pushing with When two students are pushing with
unequalunequal forces in opposite directions, a net forces in opposite directions, a net
force occurs in the direction of the larger force occurs in the direction of the larger
force.force.

The net force that moves the box will be The net force that moves the box will be
the difference between the two forces the difference between the two forces
because they are in because they are in oppositeopposite directions. directions.

They are considered to be unbalanced They are considered to be unbalanced
forces.forces.

16. Unbalanced ForcesUnbalanced Forces

The students are The students are
pushing on the box in pushing on the box in
the same direction.the same direction.

These forces are These forces are
combinedcombined, or added , or added
together, because together, because
they are exerted on they are exerted on
the box in the same the box in the same
directiondirection..

17. Unbalanced ForcesUnbalanced Forces

The net force The net force
that acts on that acts on
this box is this box is
found by found by addingadding
the two forces the two forces
together.together.

18. Inertia and MassInertia and Mass

InertiaInertia is the tendency of an object to is the tendency of an object to
resist any change in its motionresist any change in its motion

If an object is moving, it will have If an object is moving, it will have
uniformuniform motion. motion.

It will keep moving at the same speed It will keep moving at the same speed
and in the same direction unless an and in the same direction unless an
unbalancedunbalanced force acts on it force acts on it

19. Inertia and MassInertia and Mass

The velocity of the object remains The velocity of the object remains
constantconstant unless a force changes it. unless a force changes it.

If an object is at rest, it tends to If an object is at rest, it tends to
remain at rest. Its velocity is remain at rest. Its velocity is zerozero
unless a force makes it move.unless a force makes it move.

The inertia of an object is related to its The inertia of an object is related to its
mass. The greater the mass. The greater the massmass of an of an
object is, the greater its inertiaobject is, the greater its inertia

20. What happens in a crash?What happens in a crash?

The law of inertia can The law of inertia can
explain what happens in a explain what happens in a
car crash.car crash.

When a car traveling When a car traveling
about 50 km/h about 50 km/h collidescollides
head-on with something head-on with something
solid, the car crumples, solid, the car crumples,
slows down, and stops slows down, and stops
within approximately 0.1 within approximately 0.1
s.s.

21. What happens in a crash?What happens in a crash?

Any passenger not wearing a safety belt Any passenger not wearing a safety belt
continues to move continues to move forwardforward at the same speed at the same speed
the car was traveling.the car was traveling.

Within about 0.02 s (Within about 0.02 s (1/501/50 of a second) after of a second) after
the car stops, unbelted passengers slam into the car stops, unbelted passengers slam into
the dashboard, steering wheel, windshield, or the dashboard, steering wheel, windshield, or
the backs of the front seats.the backs of the front seats.

The force needed to slow a person from 50 The force needed to slow a person from 50
km/h to zero in 0.1 s is equal to km/h to zero in 0.1 s is equal to 1414 times the times the
force that gravity exerts on the person. force that gravity exerts on the person.

22. What happens in a crash?What happens in a crash?

The belt loosens a little as it restrains The belt loosens a little as it restrains
the person, increasing the time it takes the person, increasing the time it takes
to slow the person down.to slow the person down.

This reduces the This reduces the forceforce exerted on the exerted on the
person.person.

The safety belt also prevents the The safety belt also prevents the
person from being person from being thrownthrown out of the out of the
car.car.

23. Safety BeltsSafety Belts

Air bags also reduce injuries in car Air bags also reduce injuries in car
crashes by providing a crashes by providing a cushioncushion that that
reduces the force on the car's occupants.reduces the force on the car's occupants.

When impact occurs, a chemical When impact occurs, a chemical reactionreaction
occurs in the air bag that produces occurs in the air bag that produces
nitrogen gas.nitrogen gas.

The air bag expands rapidly and then The air bag expands rapidly and then
deflates just as quickly as the deflates just as quickly as the nitrogennitrogen
gas escapes out of tiny holes in the bag.gas escapes out of tiny holes in the bag.

24. Newton’s First LawNewton’s First Law

Newton’s First Law of MotionNewton’s First Law of Motion

““Law of Inertia”Law of Inertia”

InertiaInertia

tendency of an object to resist any change tendency of an object to resist any change
in its motionin its motion

increases as mass increasesincreases as mass increases

25. Concept Test 1Concept Test 1
TRUE or FALSE?TRUE or FALSE?
The object shown in the diagram must be at The object shown in the diagram must be at
rest since there is no net force acting on it.rest since there is no net force acting on it.
FALSE! A net force does not FALSE! A net force does not
cause motion. A net force cause motion. A net force
causes a causes a changechange in motion, or in motion, or
acceleration.acceleration.
Taken from “The Physics Classroom” © Tom Henderson, 1996-2001.

26. Concept Test 2Concept Test 2
You are a passenger in a car and not wearing your You are a passenger in a car and not wearing your
seat belt. seat belt.
Without increasing or decreasing its speed, the Without increasing or decreasing its speed, the
car makes a sharp left turn, and you find yourself car makes a sharp left turn, and you find yourself
colliding with the right-hand door. colliding with the right-hand door.
Which is the correct analysis of the situation? ...Which is the correct analysis of the situation? ...

27. ConcepTest 2ConcepTest 2
1. 1. Before and after the collision, there is a Before and after the collision, there is a
rightward force pushing you into the door. rightward force pushing you into the door.
2. Starting at the time of collision, the door 2. Starting at the time of collision, the door
exerts a leftward force on you. exerts a leftward force on you.
3. both of the above 3. both of the above
4. neither of the above4. neither of the above
2. Starting at the time of collision, 2. Starting at the time of collision,
the door exerts a leftward force the door exerts a leftward force
on you. on you.

28. FrictionFriction

FrictionFriction

force that force that opposesopposes motion between 2 motion between 2
surfacessurfaces

depends on the:depends on the:

types of types of surfacessurfaces

forceforce between the between the surfaces surfaces

29. FrictionFriction

Friction is greater...Friction is greater...

between between roughrough surfaces surfaces

when there’s a greater when there’s a greater
forceforce between the between the
surfaces surfaces
(e.g. more weight)(e.g. more weight)

Pros and Cons?Pros and Cons?

30. Assessment: Assessment:

31. ADDITIONAL ACTIVITIESADDITIONAL ACTIVITIES
For 20 pointsFor 20 points
Write situation/ examples where the Write situation/ examples where the
presence of forces are beneficial.presence of forces are beneficial.