Transcript Unit 7 Lesson 1 Forces

OBJECTIVES
SEC II
1. Describe forces & explain how forces act on
objects
2. Determine the net force when more than one
force is acting on an object
3. Compare balanced and unbalanced forces
4. Describe ways that unbalanced forces cause
changes in motion
II. WHAT IS A FORCE?
A. FORCE= A PUSH OR A PULL
1. Has both size and direction
2. Can change the acceleration (speed or direction)of
an object
3. newton (N) = units force is measured in
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Remember: 1 N = 100g
B. FORCES ACTING ON OBJECTS
1. All forces act on an object
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You cannot push or pull on nothing
2. Applying a force does NOT mean that there has to be
motion
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Pushing against the wall
Sitting in a chair
3. Forces can be unseen
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Static electricity
Gravity
Magnetism
C. DETERMINING NET FORCE
1. Net force= combination of all forces acting on an
object
2. Forces in the same direction will be added together
to figure out the net force
3. Forces in the opposite direction will be subtracted
from each other to get the net force
4. Balanced forces = zero
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When the forces are equal in opposite directions
There is no movement
Sitting on a chair
5. Unbalanced forces produce a change in motion
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Change in motion could be speed or direction
Fnet does NOT equal 0 N
Cause an unmoving object to move
III. FRICTION: A FORCE THAT OPPOSES MOTION
BETWEEN 2 SURFACES THAT ARE IN CONTACT
A. THE SOURCE OF FRICTION
HTTPS://YOUTU.BE/MIB7HZUVMM0
1. Surface of any object is rough (even if it feels
smooth)
2. When 2 surfaces come into contact with each
other they will “stick together”
Microscopic hills and crevices “stick & slip”
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3. 2 factors that effect the amount of friction:
a. The force pushing the surfaces together
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the more weight the more force pushing down the more
friction
b. How rough the surface is
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rougher equals more friction
because of more “hills &
valleys” to cause the
“stick & slip”
B. TYPES OF FRICTION:
HTTPS://YOUTU.BE/VUFQJSEEZNG
1. Kinetic friction: friction between moving surfaces
a. Sliding friction is usually greater than rolling friction
(depending on the surface)
• Breaks on a car or bike
• Writing with a pencil
b. Rolling friction is used in transportation
2. Static friction: force applied to an object but does
not cause the object to move
a. Static means= not moving
b. Force of the static friction balances the applied
force
• Leaning an object against the wall and it
doesn’t fall
c. Static friction can be overcome with a large
enough force
d. As soon as movement occurs static friction
disappears & kinetic friction immediately occurs
HTTPS://YOUTU.BE/AX_LCOJLCTO (PHONE BOOK FRICTION)
HTTPS://YOUTU.BE/QMW_UYWWHWQ
C FRICTION: HELPFUL OR HARMFUL???
1. Without friction it would
be hard to walk, drive a
car, or write on paper
2. Friction wears down
engine parts, can cause
“rug” burns, & leads to
erosion of land
3. To reduce friction lubricants are
used
a. Substances that are applied to
surfaces to reduce friction
b. Motor oil in an engine
c. Air on an air hockey table
d. Sanding wood
4. To increase friction
you could increase
the force used to
push against
something
5. Making the surface
rough also increases
friction
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Rosin
Batting gloves
Sand/salt on icy roads