8.PS.2-5-Topic 1 & Topic 2

​8.PS.2-5
Topic 1-Forces & Motion
Topic 2-Net Force

By Jessica Freeman

​force

​move

stays the same

change motion

Forces

• friction and gravity are always acting on us in our everyday lives

• we'll talk about both types of forces on their own later

Normal force is OPPOSITE gravity. It pushes upward from the surface to the object and prevents things from falling through whatever they are resting on.​

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​Normal Force (F_n)

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Multiple Choice

Which force pushes things down towards the center of the earth?

• Gravity

• Normal

• Applied

• Friction

Multiple Choice

Which force is opposite gravity and keeps us from falling through everything?

• Gravity

• Normal

• Applied

• Friction

​Forces that are applied by people or other things. The arrow will face the direction of the force being applied.

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Examples: pushing a box, driving a car, pulling a door.

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​​Applied force (F_a)

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​Two surfaces rubbing together create friction. This force is OPPOSITE applied forces.

The arrow will face opposite of the applied force.​

​​Friction (F_f)

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​A diagram that shows the forces on an object is called a free body diagram.

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Draw the picture below on a paper to use as a reference for the next couple of questions! Or scroll back to this slide if you can.​

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​Free body diagram

Multiple Choice

Hunter is pushing a box, what kind of force is he creating?

• Gravity

• Normal

• Applied

• Friction

Multiple Choice

Hunter's box is sliding on the carpet. What force is opposing the force created by him pushing the box?

• Gravity

• Normal

• Applied

• Friction

Multiple Choice

The force that keeps objects on top of surfaces instead of letting them sink into the surface is known as:

• normal

• abnormal

• static

• inertia

Multiple Choice

Name the missing force...

• frictional force
• weight force
• thrust
• buoyant force

Multiple Choice

Name the missing force...

• weight force
• normal force
• applied force
• frictional force

Multiple Choice

Name the missing force.

• Normal Force

• Friction Force

• Gravitational Force

• Applied Force

• ​change in motion.

  • unbalanced force can be in opposite directions or the same direction​

​When forces are unbalanced

• motion is constant

• there is no motion​

​When forces are balanced

​Balanced and Unbalanced Forces

balanced forces are equal. unbalanced forces are not equal​

100N​

75N​

75N​

75N​

Multiple Choice

Which of these is evidence that an unbalanced force is acting on an object?

• The mass of the object is changing

• The object remains at rest.

• The motion of the object is changing

• The object continues moving in a straight line at constant velocity.

sum

add

subtract

15

​When forces are unbalanced, the net force > 0

​When forces are balanced the net forces = 0

​Net force is the SUM of all forces acting on an object

balanced forces are equal. unbalanced forces are not equal

100N​

75N​

75N​

75N​

Multiple Choice

Which of these is evidence that an unbalanced force is acting on an object?

• The mass of the object is changing

• The object remains at rest.

• The motion of the object is changing

• The object continues moving in a straight line at constant velocity.

​When forces are unbalanced, the net force > 0

​When forces are balanced the net forces = 0

​Net force is the SUM of all forces acting on an object

balanced forces are equal. unbalanced forces are not equal

100N​

75N​

75N​

75N​

​the Newtons that are going in the SAME DIRECTION

​​Add

​ the Newtons that are going in the OPPOSITE DIRECTION

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​​Substract

​How to calculate Net Force

​Remember:

1. Determine the direction and magnitude of each individual force first​

2. when subtracting, subtract the smaller number from the larger number

​LET'S DO SOME PRACTICE

Open Ended

What is the magnitude AND direction of each individual force?

Open Ended

Are these forces acting in the same direction or opposite direction?

Open Ended

To find the net force, will we add or subtract?

Multiple Select

What is the net force (direction and magnitude) on this object?

• 4N

• Left

• Right

• 0N

• No direction since the forces are balanced

Multiple Choice

What is the net force (direction and magnitude) acting on the box?

• 30N, right

• 30N, left

• 5N, left

• 25N, left

Multiple Choice

What is the net force (direction and magnitude) acting on the box?

• 100N, left

• 90N, right

• 100N, right

• 140N, right

Multiple Choice

Looking at all four boxes, which box is experiencing a net force of 0N?

• A

• B

• C

• D

Multiple Choice

Looking at the boxes, which box is experiencing a net force of 3N, down?

• A

• B

• C

• D

Multiple Choice

The following picture shows forces acting on a sneaker. Suppose that the sneaker is moving toward the spring scale.

Based on evidence in the picture, in which direction is the sum of all the forces (the net force) acting?

• The net force is acting in an upward direction.

• The net force is acting in a downward direction.

• The net force is acting to the left.

• The net force is acting to the right.

Unbalanced Forces

•Unequal forces that cause a change in an
object’s motion

•Cause a change in speed and/or direction of an
object – moves the direction of the greater force

100 N

50 N

Multiple Choice

Is this an example of balanced or unbalanced forces?

• Balanced

• Unbalanced

Unbalanced Forces

•Unequal forces that cause a change in an
object’s motion

•Cause a change in speed and/or direction of an
object – moves the direction of the greater force

100 N – 50 N = 50 N

100 N

50 N
UNBALANCED

Unbalanced Forces Examples

• A football player tackling a quarterback

• Pushing a lawnmower across the yard

• A skydiver falling toward the ground

• Any object that is speeding up, slowing down,

or changing direction (accelerating)

Forces are unbalanced when the net force

does not equal 0 Newtons

Fill in the Blanks

Multiple Choice

What direction will the box go?

• Left

• Right

Multiple Choice

Are the forces on the plan balanced or unbalanced

• Balanced

• Unbalanced

Multiple Select

Which direction will the airplane move? Select all that apply

• Left

• Down

• Up

• Right

Fill in the Blanks

Fill in the Blanks