Forces in Motion

• ​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.

​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

​

​​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

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.

What is a FORCE?

• A force is a PUSH or a PULL

• Forces are measured in a unit called NEWTONS

• You use a SPRING SCALE to measure force

• Forces are categorized into two groups: CONTACT or NON-CONTACT

Multiple Choice

What is the tool used to measure FORCE?

• balance

• spring scale

• weight

CONTACT FORCES

A force that can cause or change motion of an object by touching it. 

Examples of Contact Forces:

•Applied Force

•Normal Force

•Friction

•Air Resistance

CONTACT FORCES

The image shows a baker pushing his hands into dough, causing the top of the dough to accelerate downward. You can see the baker's hand and dough come into contact with each other. A contact force is a push or a pull applied by one object to another object that is touching it. Contact forces are also called mechanical forces. 

APPLIED FORCE

An applied force is when one object directly pushes or pulls on another. For example, pushing or pulling a door, texting or using a phone, writing, stirring a pot when you cook, a tug of war, etc. (Draw one example in your notes.)

Can you think of any other examples of an applied force?

NORMAL FORCE

A normal force is a support force that touches another object which is stable or not moving. For example, if a book is resting upon a surface like a table, then the surface is exerting an upward force upon the book in order to support the weight of the book. (Draw the picture in your notes.)

Can you think of any other examples of a normal force?

FRICTION

Why does the baseball player slow down as he is sliding towards home plate? FRICTION!

Friction is a contact force that resists the sliding or forward motion between two objects. The force of friction opposes motion, as seen by the blue arrow in the picture. Rougher surfaces will produce greater friction, while smoother surfaces reduce the force or friction.

Can you think of any other examples of friction?

FRICTION

Let's put this to the test.

1. Rub your hands together quickly for 15 seconds.

2. Next, apply hand sanitizer, water, or lotion to your hands.

3. Now, rub your hands together quickly for 15 seconds.

Did you notice a difference? What caused this to occur?

AIR RESISITANCE

Would you jump out of a plane without a parachute? Probably NOT!

Air resistance is a type of frictional force that acts upon objects as they travel through the air. As the canopy of the parachute opens, air gets trapped inside. The air pushes up on the parachute, while gravity is pulling you down. The opposing force of the air causes you to slowly fall.

QUIZ TIME!

Let's see how much you have learned.

Multiple Choice

What is the type of contact force that is being described?

A foot kicking a soccer ball

• Applied Force

• Normal Force

• Friction

• Air Resistance

Multiple Choice

What is the type of contact force that is being described?

The soccer ball slowing down as it rolls across the field.

• Applied Force

• Normal Force

• Friction

• Air Resistance

Multiple Choice

What is the type of contact force that is being described?

The soccer ball resting on the ground.

• Applied Force

• Normal Force

• Friction

• Air Resistance

Multiple Choice

What is the type of contact force that is being described?

Your hand being pulled backwards as you stick it out of the window of a moving car.

• Applied Force

• Normal Force

• Friction

• Air Resistance

Multiple Choice

Forces applied when the objects involved are in direct contact.

• Contact forces

• Normal forces

• action-at-a-distance forces

Multiple Choice

The upward force acting on the parachute is called ______________.

• Force of friction

• Force of gravity

• Normal force

• Air resistance

Multiple Choice

What force are you demonstrating when you pull a cup towards you?

• Gravitational Force

• Normal Force

• Applied Force

• Friction

Multiple Choice

What type of force is being applied to the car by the person?

• applied force

• normal force

Multiple Choice

What type of force is acting on the student and the chair?

• applied force

• normal force

• frictional force

Multiple Choice

This type of force is when one object pushes or pulls on another object by touching it

• Applied

• gravity

• magnetic

• normal

Multiple Choice

A type of friction that occurs when air pushes against a moving object causing it to decelerate.

• friction

• air resistance

• velocity

• gravity

Multiple Choice

Friction is a force that acts in an ___________ direction of movement.

• similar
• opposite
• parallel
• west

Gravity

physical science

NOTICE

MASS STAYS THE SAME!!! An object's mass will be the same, no matter where it is or how much gravity there is.

Multiple Select

SELECT ALL THAT APPLY

How are mass and weight different?

• mass never changes

• weight depends on gravity

• mass depends on gravity

• weight never changes

Multiple Choice

What is acceleration due to gravity on Earth?

• 98 m/s²

• 9.8 m/s²

• 0.98 m/s²

Equation w = mg

how to solve various problems

Multiple Choice

If a bike has a mass of 10.5 kg, how much does it weigh on Earth?

• 102.9 N
• 1.07 N
• 10.5 N
• 0.93 N

Multiple Choice

The Mars Rover Curiosity weighs 8810.2 N on Earth. Determine Curiosity's mass.

• 899 kg
• 86,339.96 kg
• 0.001 kg
• 8810.2 kg

Multiple Choice

If an object weighs 35 N on Saturn, what is the mass of the object if gravity is equal to 10.44 m/s²?

• 3.35 kg
• 365.4 kg
• 0.298 kg
• 35 kg

Multiple Choice

If a 75 kg TV is taken to Venus, where it weighs 665 N, what is acceleration due to gravity on Venus?

• 8.87 m/s²

• 49,875 m/s²

• 0.11 m/s²

Multiple Choice

An astronaut has a mass of 100 kg and has a weight of 370 N on Mars. What is the gravitational strength on Mars?

• 37,000 m/s²

• 3.7 m/s²

• 0.27 m/s²

Multiple Choice

How much does Captain America weigh if he has a mass of 86.18 kg?

• 844.56 N
• 86.18 N
• 8.79 N
• 0.11 N