CST Review_Force

CST ReviewForce

CST Review

Forces

BrainPopGravity

Brain Pop

http://www.brainpop.com/science/motionsforcesandtime/gravity/

BrainPopBuoyancy

Brain Pop

http://www.brainpop.com/science/motionsforcesandtime/buoyancy/

Force Graphic Organizer

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Special Forces Graphic Organizer

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Cornell NotesTitle: Buoyancy

Questions Notes (Answers)

II. Buoyancy is the force of a liquid pushing up on an object.A. Buoyant force balances the force of gravity when an

object floats.

Question 2:What are buoyant

forces?

Buoyant Force of water pushes up.

Force of Gravity pushes down.

B. Weight is the pull of gravity on an object.

Study



Question 3:What determines the

strength (magnitude) of buoyant force?

III. The buoyant force is equal to the weight of liquid an object displaces (pushes out of the way).

A. The weight of the displaced liquid is the same as the weight of the object under the liquid.

B. The part of the object above the liquid DOES NOT MATTER.

Buoyant Force

Weight of Displaced

Water

Study



C. When an object is flat buoyancy is greater because it displaces more liquid. Buoyant force pushes up against a larger surface area.

Buoyant Forces of liquid push up.

Question 3:What determines the

strength (magnitude) of buoyant force?

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CST Review Questions

How is force described?II. Force has a strength

(magnitude) and a direction.

How do forces add and subtract?A. Forces pushing or pulling in

the same direction add.

+

These forces add.

1 N right

1 N right

How do forces add and subtract?B. Forces pushing or pulling in

opposite directions subtract.

These forces subtract so the box doesn’t move.

_1 N right 1 N left


.5cm = 2N


3.0 cm ?

0.5 cm = 2N


3.0 cm 12N

0.5 cm = 2N


3.0 cm 12N

3.5 cm ?

0.5 cm = 2N


0.5 cm = 2N

3.0 cm 12N

3.5 cm 14N


.5cm = 2N

3.0 cm = 12N3.5 cm = 14 N


____________________________________________

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______________________


____________________________________________

___________________________________________

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What will make you have to push harder?



less friction?



mass ?

VIII. When an object has more mass, it requires a greater force to make it move.

How does mass affect force?

500 N Right

Books = 800 kg

5 N Right

Leaves = 8 kg

A. If something is heavier, you have to push harder to move it.


Mass of Feathers = 1 kg

Mass of Bricks = 1000 kg

2000 N Right

2 N Right

Distance moved = 5 feet



harder or easier to push?



easier to push

harder to push



less friction?

easier to push

harder to push

XII. Friction is a force which slows down or stops an object’s motion.

What is Friction?

50 N Right

Force of friction of the wheels on the road 20 N Left

Force of the Boy pedaling his bicycle forward.

A. Friction always goes in the opposite direction of the force causing the motion.

What is Friction?

40 N Right 190 N Left

Friction slowing down motion

Force causing motion

B. Friction is caused by objects or materials rubbing against each other.

What is Friction?

Friction of Air rubbing against an

airplane.Friction of wheels on the

road

Friction of metal on snow.

Friction of hands rubbing

together.



harder or easier to push?

easier to push

harder to push



easier to push

harder to push

easier to push

easier to push



harder to push

Buoyant Forces

Consider This

XI. Buoyancy is the force of a liquid pushing up on an object.

What are buoyant forces?


A. Buoyant force is equal to gravity when an object floats.



Force of Gravity pushes down.

B. When an object is flat, Buoyancy is greater because the liquid pushes up against a larger surface area.


Buoyant Forces of liquid push up.

Force

Review

Think-Group-Share1. THINK: Read the question and THINK

about the answer.

2. GROUP: Discuss the answer with your teammates and agree on the correct answer.

3. SHARE your answers by writing them on the magnetic slate and holding them up.

Think-Group-Share

What is force?

Think-Group-Share

What is force?

a push or pull

How is force described?I. Force is a push or pull.

Think-Group-Share

What does force change?

A. the mass of an object

B. the motion of an object

C. the volume of an object

What is force?B. Force changes the motion of something

by changing its speed or direction.

Think-Group-Share

Force is measured in

A. Grams

B. Meters

C. Newtons

D. Liters

How is force described?B. Force strength is measured in Newtons (N) (after Isaac Newton).

Think-Group-Share

What 2 things does force have?

A. magnitude and direction

B. size and shape

C. strength and shape

How is force described?II. Force has a strength

(magnitude) and a direction.

Think-Group-Share

A weight lifter raises his barbells straight up with a force of 30 Newtons. How would you describe the force?

Think-Group-Share

A weight lifter raises his barbells straight up with a force of 30 Newtons. How would you describe the force?

30 N Up

Think-Group-Share

What do forces in the same direction do?

A. subtract

B. cancel each other

C. add

How do forces add and subtract?A. Forces pushing or pulling in

the same direction add.

+

These forces add.

1 N right

1 N right

Think-Group-Share

What do forces in opposite directions do?

A. subtract

B. cancel each other

C. add

How do forces add and subtract?B. Forces pushing or pulling in

opposite directions subtract.

Opposite forces subtract.

_1 N right1 N left

What is the force? Will the rope move?

Think-Group-Share

The force left after all forces have been added and subtracted is called

A. final force

B. net force

C. resultant force

What is net force?IV. The force left after all forces

have been added and subtracted is the net force.

=

These forces subtract.

_Zero Net force

1 N right 1 N left

Think-Group-Share

A boy pushes a cart with a force of 3 N right. Another boy pushes the same cart with a force of 1 N left. What is the net force on the cart?

Think-Group-Share

A boy pushes a cart with a force of 3 N right. Another boy pushes the same cart with a force of 1 N left. What is the net force on the cart?

3 N right - 1 N left = 2 N right

Think-Group-Share

A man pushes a car with a force of 10 N right. Another man helps him push the car with a force of 9 N right. What is the net force on the car?

Think-Group-Share

A man pushes a car with a force of 10 N right. Another man helps him push the car with a force of 9 N right. What is the net force on the car?10 N right + 9 N right = 19 N right

Think-Group-Share

When opposite forces on an object are equal, the forces are

A. balanced

B. unbalanced

What are balanced forces?V. When the opposite forces on an object

are equal, the forces are balanced.

Balanced Forces

=1 N right 1 N left

Think-Group-Share

When opposite forces on an object are NOT equal, the forces are

A. balanced

B. unbalanced

What are unbalanced forces?VI. When the opposite forces on an

object are not equal, the forces are unbalanced.

Unbalanced Forces

1 N right

1 N left

2 Newtons of force 1 Newton of force

1 N right

Think-Group-Share

When forces on an object are balanced, the object

A. does not move

B. moves

C. changes form

What are balanced forces?B. When the forces are balanced, the

object does not move. (Its motion does not change).

Balanced Forces Net Force = 0

=1 N right 1 N left

Net force = 0

Think-Group-Share

When forces on an object are unbalanced, the object

A. does not move

B. changes form

C. changes its motion

What are unbalanced forces?B. Unbalanced forces cause an object

to change its direction or motion (speed up or slow down).

=

Objects move because of unbalanced forces

1 N right

1 N right

1 N right

Think-Group-Share

A boy pulls a wagon with a force of 35 N left. The wind pushes the wagon with a force of 20 N right. Are the forces balanced or unbalanced?

Think-Group-Share

A boy pulls a wagon with a force of 35 N left. The wind pushes the wagon with a force of 20 N right. Are the forces balanced or unbalanced?

unbalanced

Think-Group-Share

A girl pulls on a rope with a force of 15N left. Her friend pulls on the rope with a force of 15 N right. Are the forces balanced or unbalanced?

balanced

Think-Group-Share

Friction is the force A. of objects rubbing against each other

B. which pulls objects together

C. which changes the shape of objects until it is removed.

D. of liquids pushing up on an object.

B. Friction is caused by objects or materials rubbing against each other.

What is Friction?

Friction of Air rubbing against an

airplane.Friction of wheels on the

road

Friction of metal on snow.

Friction of hands rubbing

together.

Think-Group-Share

Friction

A. Goes in the same direction as the motion of the object.

B. Goes in the opposite direction of the motion of the object.

C. Has nothing to do with the motion of the object.

B. Friction always goes in the opposite direction of the force causing the motion.

What is Friction?

40 N Right 190 N Left

Friction slowing down motion

Force causing motion

Think-Group-Share

A girl pedals her bike forward with a force of 20N. The wind pushes her forward with a force of 10N. The friction on her wheels exerts a force of 5N backwards. What is the net force?

Think-Group-Share

A girl pedals her bike forward with a force of 20N. The wind pushes her forward with a force of 10N. The friction on her wheels exerts a force of 5N backwards. What is the net force?

20N Forward

10N Forward

20N forward + 10N forward – 5N backwards = 25N forward

5N Backwards

Think-Group-Share

Gravity is the force A. of objects rubbing against each other




III. Gravity is the force that pulls objects toward each other.

What is gravity?

Think-Group-Share

Gravity

A. Compresses and stretches objects.

B. makes objects fall down.

C. slows the motion of objects.

D. makes objects float.

B. Objects fall down because the Earth’s gravity pulls them down.

What is gravity?

GRAVITY

Earth’s gravity is a force pulling objects down toward the center of the Earth.

Think-Group-Share

Objects with greater mass

A. have more gravity.

B. have less gravity.

C. have no gravity.

How does the Sun hold the solar system together?

A. Objects with bigger mass, exert a greater force of gravity on other objects.

How does the Sun hold the solar system together?

B. The Sun’s gravity is extremely strong because its mass is EXTREMELY large.

Newton’s 2nd Law says: greater mass = greater gravity.

Think-Group-Share

Gravity gives stars and planets

A. more mass.

B. less mass.

C. their shapes.

D. greater energy.

C. Gravity give stars, planets, and the solar system their shapes.

What is gravity?

Think-Group-Share

Elastic Force is the force A. of objects rubbing against each other




IX. Elastic forces change the shape of an object. But when the force is removed, the object regains its shape.

What are elastic forces?

Leaves = 8 kg

10 N Up & Left

Think-Group-Share

Friction





Friction is a force that slows down or stops an object’s motion.

What is Friction?

50 N Right

Force of friction of the wheels on the road 20 N Left

Force of the Boy pedaling his bicycle forward.

Think-Group-Share

Elastic Force





A. Some elastic forces stretch the object.


10 N Up & Left

10 N Up & Left

B. Some elastic forces squeeze or compress the object.


2 N Down

2 N Right 2 N Left

2 N Down

2 N Up

Think-Group-Share

Elastic Forces that squeeze an object are called

A. friction

B. tension.

C. compression.

D. gravity.

C. Elastic forces that squeeze are called compression.


2 N Down

2 N Right 2 N Left

2 N Down

2 N Up

Think-Group-Share

Elastic Forces that stretch an object are called

A. friction

B. tension.

C. compression.

D. gravity.


D. Elastic forces that stretch an object are called tension.

Think-Group-Share

Buoyancy is the force A. of objects rubbing against each other



D. of a liquid or gas pushing up on an object.

XI. Buoyancy is the force of a liquid or gas pushing up on an object.



Think-Group-Share

Buoyancy





A. Buoyancy makes objects float.What are buoyant forces?


Think-Group-Share

Buoyant force is

A. equal to the weight of the object.

B. equal to the weight of the liquid displaced by the object.

III. The buoyant force is equal to the weight of liquid an object displaces (pushes out of the way).


Buoyant Force

Weight of Displaced

Water

Draw this diagram.

Think-Group-Share

Objects with greater mass

A. need no force to move

B. need less force to move

C. need more force to move

Think-Group-Share

Objects with less mass

A. need no force to move

B. need less force to move

C. need more force to move

VIII. When an object has more mass, it requires a greater force to make it move.


500 N Right

Books = 800 kg

5 N Right

Leaves = 8 kg

Special Forces Practice Problems

A box has a mass of 325 kg. Another box has a mass of 95kg. Which box will need a greater force to lift it?

325 kg 95

kg

Special Forces Practice Problems

The box with the greater mass needs more force to lift it.

325 kg

95 kg

A box has a mass of 325 kg. Another box has a mass of 95kg. Which box will need a greater force to lift it?

The 325 kg box.

CST Review_Force

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