Transcript of Science Focus Lesson SC.5.P.13.2 Net Forces Polk County Public Schools.
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- Science Focus Lesson SC.5.P.13.2 Net Forces Polk County Public
Schools
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- SC.5.P.13.2 Benchmark: Investigate and describe that the
greater the force applied to it, the greater the change in motion
of a given object. Essential Question: What is the difference
between balanced and unbalanced forces? Vocabulary: balanced forces
force unbalanced forces net force
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- What is Force? A force is a push or pull on an object Every
force has a STRENGTH Every force has a DIRECTION Forces work in
pairs, every force has an opposing force working in the opposite
direction
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- How do forces affect objects? Forces can affect objects in
several ways Forces can set an object in motion Forces can change
an moving objects speed and/or direction A force can also affect an
object without making it move!
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- More than one force usually acts on an object at the same time
Sometimes forces are applied in the same direction Sometimes forces
are applied in different directions Balanced forces produce no
change in the motion of an object Unbalanced forces produce a
change in the motion of an object How do forces affect
objects?
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- Balanced Forces Balanced forces are opposing forces of the same
strength acting on an object Balanced forces result in NO CHANGE in
the motion of an object Think about a game of tug-of-war. If there
is equal pull on both sides, then each side is balanced and neither
side will fall forward!
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- Balanced Forces Balanced forces do not cause a change in the
motion of objects
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- Balanced forces at work: The window arches of the Roman
Coliseum. The blocks in the window arches work together, exerting
force against each other, thereby holding each other up. This is an
example of balanced forces.
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- Unbalanced Forces Unbalanced forces are opposing forces of
unequal strength acting on an object Unbalanced forces always CAUSE
A CHANGE in motion. Think about a game of tug-of-war. If there is
an unequal pull, then there are unbalanced forces and one side will
fall forward!
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- Unbalanced Forces Unbalanced Forces happen when unequal forces
act on an object
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- When you ride a bike the force of the friction of the tires
against the road is greater than the opposing force of friction
with the air. The bicycle moves forward. This is an example of
unbalanced forces. Unbalanced forces at work: A bicycle rider
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- Summarizing Think-Pair-Share Think: How do you know when forces
are balanced? unbalanced? Pair: Turn to your shoulder partner
Share: Partner A describe balanced forces to partner B. Partner B
describe unbalanced forces to partner A.
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- What is Net Force? A net force is the sum of all forces acting
on an object. A net force is capable of accelerating a mass.
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- When net forces on each side are not equal, the object moves in
the direction of the greater force. Example: The force exerted by
Linus, on the right, is greater than the force exerted by Charlie
Brown, on the left. Therefore the net force is greater on the right
and the see-saw moves in the direction of the greater net
force.
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- Forces can act in the same direction If two forces act on an
object in opposite directions and the same force is not applied on
each side, the difference in the forces is the net force. 12 N 10 N
= 2 N of force to the right If two(or more) forces act on an object
in the same direction, the net force is the sum of the forces. 25 N
+ 20 N = 45 N of force to the right Forces can act in opposite
directions
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- Whenever the net force is equal to zero, the object does not
change its motion. When forces cancel each other out, the net force
is zero. The object does not change its motion. The car has zero
motion. The forces acting on it are of equal strength and opposite
in direction. There is a net force of zero and the car does not
change its motion. A space probe maintains both its speed and
direction. The forces acting on it are of equal strength and
opposite in direction. There is a net force of zero and the space
probe does not change its motion.
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- Summarizing Explain how net forces determine the change in the
motion of an object.
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- Guided Practice 1. A 3 Newton force is applied to the left side
of a moose, and a 7 Newton force is applied to the right side of a
moose. In which direction would the moose move based on the forces
applied? A. right B. left C. no movement D. up
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- The moose would move to the left because there is a greater
force being applied on the right side.
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- 2. A woman at a grocery store applies an unbalanced force to a
shopping cart. Which of the following things would happen? A.The
shopping cart will start to move. B.The shopping cart does not
move. C.The shopping cart gets smaller. D.The shopping cart gets
bigger.
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- Unbalanced forces always cause a change in motion.
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- 3. A car is not moving. A balanced force is applied to it. What
happens to the car? A. It starts to move slowly, then faster B. It
does not move C. It moves backwards D. It starts to accelerate
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- Balanced forces do NOT cause a change in the motion of
objects.
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- 4. In a tug of war contest, one person pulls with a force of 5
Newtons. Another person on the same team pulls with a force of 3
Newtons. In order for the force of the rope to be balanced, what
force would the other team be pulling with? A. 2 Newtons B. 5
Newtons C. 8 Newtons D. 15 Newtons
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- For forces to be balanced they must be equal and opposite. If
one side pulls with a combined force of 8 Newtons, the other side
would also need to pull with a combined force of 8 Newtons in order
for the forces to be balanced.
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- Turn to your shoulder partner and give examples of balanced and
unbalanced forces. Switch roles. Summary Question
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- Check Your Understanding 1. When an object is at rest, which of
the following is true? a. There are no forces acting on it. b.
There are forces acting on it, but these forces are balanced. c.
There is just one force acting on it, which is gravity. d. The
forces acting on it are unequal in strength
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- Check Your Understanding 2. A girl is standing still on a
tennis court, with her racket resting on her shoulder. Her tennis
partner just hit a ball to her. Which object is showing the effect
of an unbalanced force? a. The girl standing still b. The tennis
racket c. The ball d. The ground
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- Check Your Understanding 3. Jennifer used a basketball to show
how energy can be applied to the ball to produce motion. Which
action would NOT produce motion by applying energy to the ball? A.
She threw the ball to the floor and it bounced back into the air.
B. She pitched the ball through the air and it flew into the hoop.
C. She held the ball steady on the gym floor with her right foot.
D. She placed the ball on the top shelf of a locker when she was
finished with it.
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- Check Your Understanding 4. Why does it take more force to move
a heavy box up a ramp than to move the same box down the ramp? A.
There is more friction on the bottom of the box when going up a
ramp. B. Gravity is pushing the box up the ramp at the same time
you are pushing the box up the ramp. C. You are exerting force from
both your arms and legs when you are pushing the box up the ram. D.
When you push an object up a ramp, you are working against gravity
which pulls the box towards the ground.
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- Check Your Answers 1. B - There are forces acting on it, but
these forces are balanced. 2. C- The ball 3. C- She held the ball
steady on the gym floor with her right foot. 4. D- In order to move
a box up a ramp you must use a force greater than the force of
gravity pulling it toward the ground
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- Summarizing Answer the Essential Question in your Science
Notebook. Essential Question: When are forces balanced or
unbalanced? Give examples of each.