Force and Motion. A PUSH or a PULL is a FORCE. So, a good definition for force is a push or pull in a particular direction.

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Force and Motion

Learning Objectives

After the lesson, you should be able to:

➢ Define force and how I affect motion of objects.

➢ Use Newton's first law to explain the motion of an object.

➢ Using Newton’s second law, relate the force, mass, and acceleration of an object.

➢ Explain that forces act in pairs as described by Newton’s third law.

What is Force?

When you ride a bike, your foot pushes against the pedal. The push makes the wheels of the bike move. When you drop something, it is pulled to the ground by gravity.

A PUSH or a PULL is a FORCE. So, a good definition for force is a push or pull in a particular direction.

Forces affect how objects move. They may cause motion; they may also slow, stop, or change the direction of motion of an object that is already moving.

Forces can affect motion in several ways:

→ They can make objects start moving

→ They can make objects move faster

→ They can make objects move slower

→ They can make objects stop moving

→ They can make objects change direction

→ They can make objects change shape

Since force cause changes in the speed or direction of an object, we can say that forces cause changes in velocity, so…. Forces cause acceleration!

FORCE FACTS:

→ Forces are measured in newton (N)

→ Forces usually act in pairs

→ Forces act in a particular direction

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→ Forces usually cannot be seen, but their effects can

Label the force in each picture as a push or pull. Then describe whether the force is causing a change in speed or direction or both.

Challenge yourself!

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Balanced and Unbalanced Forces

More than one force can act on an object at a time. The forces can push or pull in any direction. What happens to the object when the forces act depends on two things:

→ How strong the forces are

→ The direction of the forces

When more than one force acts on an object, the forces combine to form a net force. The combination of all the forces acting on an object is the net force.

Forces may work together or they may be opposite forces.

Two or more opposite forces are balanced forces if their effects cancel each other and they do not cause a change in an object's motion. If two forces of equal strength act on an object in opposite directions, the forces will cancel, resulting in a net force of zero and no movement.

If the effects of the forces don't cancel each other, if one force is stronger than others, the forces are unbalanced forces. Unbalanced forces cause a change in motion; speed and/or direction.

When two forces act in the same direction on an object, the net force is equal to the sum of the two forces.

When two unequal forces act in opposite directions on an object, the net force is the difference of the two forces.

The final force and its direction are called a resultant.

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Read the previous page and USE COMPLETE SENTENCES to answer the following questions:

1. What are the two aspects of force that need to be known to determine how an object will move?

___________________________________________________________________________

2. Use your own words to define Net Force:

___________________________________________________________________________

3. Describe what happens to an object's motion when it is experiencing Balanced Forces?

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4. If the motion of an object changes, what must be true about the forces acting on that object?

___________________________________________________________________________

5. Use your own words to define Unbalanced Forces:

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6. Use your own words to define Resultant:

___________________________________________________________________________

7. Draw a picture that explains Unbalanced Forces and Resultant:

Learning Activity!

Name:___________ No. ____

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Circle the best answer in each sentences:

1. The forces shown above are PUSHING / PULLING forces.

2. The forces shown above are WORKING TOGETHER / OPPOSITE FORCES.

3. The forces are EQUAL / NOT EQUAL.

4. The forces DO / DO NOT balance each other.

5. The resultant force is 1000 N TO THE RIGHT /1000 N TO THE LEFT / ZERO.

6. There IS /IS NO motion.

7. The forces shown above are PUSHING / PULLING forces.

8. The forces shown above are WORKING TOGETHER / OPPOSITE FORCES.

9. The forces are EQUAL / NOT EQUAL.

10. The forces DO / DO NOT balance each other.

11. The stronger force is pulling to the RIGHT / LEFT.

12. The weaker force is pulling to the RIGHT / LEFT.

13. Motion is to the RIGHT / LEFT.

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NEWTON’S FIRST LAW OF MOTION

1. Newton’s first law of motion is also known as the LAW OF ______________________________.

2. Newton’s first law says that

a. an object that IS NOT MOVING, or is at ___________, will stay at____________, AND b. an object that IS MOVING will keep moving with constant __________, which means at the

same __________ and in the same____________, UNLESS c. an __________________________ force acts on that object.

3. What is inertia?

___________________________________________________________________________

__________________________________________________________________________

4. What property of an object determines how much inertia it has?

___________________________________________________________________________

5. Which of the following has more inertia?

a. Bowling ball or Tennis ball ________________________________

b. Hammer or Feather ________________________________

6. When traveling in a car and turning to the right, which way does your body go and why?

___________________________________________________________________________

Learning Activity!

Name:___________ No. ____

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NEWTON’S SECOND LAW OF MOTION

1. Newton’s second law of motion is also known as the LAW OF___________________.

2. Newton’s second law says that when an __________________ force is applied to a ________________, it causes it to ____________________________.

3. The greater the force that is applied, the ____________________ the acceleration.

4. The lesser the force that is applied, the _____________________ the acceleration.

5. If the same force is applied to an object with a large mass, it will have a ____________

acceleration.

11. If the same force is applied to an object with a small mass, it will have a ___________ acceleration.

12. The equation that is used to solve second law problems is F = ma.

a. What do each of the variables mean?

F = ______________ m = ___________ a = _________________

b. What unit of measurement must be used with each variable?

F = _________ m = _________ a = __________

Learning Activity!

Name:___________ No. ____

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PROBLEM SOLVING: NEWTON’S LAWS OF MOTION

1. How much force is needed to accelerate a 1000-kg car at a rate of 3 m/s²?

Given Work

Answer:

2. If a 70-kg swimmer pushes off a pool wall with a force of 250 N, what is her acceleration?

Given Work

Answer:

3. Find the mass of a football player who has 1250 N of force and has an acceleration of 1.5 m/s².

Given Work

Answer:

4. How much acceleration is given to a 45 kg child with a 0.75 N push on a swing?

Given Work

Answer:

5. What is the mass of a car that its going 2 m/s² and then hits a tree with a force of 6000N?

Given Work

Learning Activity!

Name:___________ No. ____

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NEWTON’S THIRD LAW OF MOTION

1. Newton’s third law of motion is also known as the LAW OF___________________________.

2. Newton’s third law says that every time there is an ______________________________ force, there is also a _______________________ force that is ______________________ in size and acts in the ____________________________ direction.

3. Newton’s third law states that forces must ALWAYS occur in ___________________________.

4. Listed below are ACTION forces. Tell the REACTION force.

a. Your bottom pushing on your desk seat __________________________________________

b. A bat hitting a baseball _______________________________________________________

c. Your finger pressing on your phone screen while texting

__________________________________________________________________________

5. What is friction?

______________________________________________________________________________

6. List the four types of friction:

a. _________________________ c. _________________________

b. _________________________ d. _________________________

7. Friction that occurs in gases and liquids is called ___________ friction.

8. True or False: Static friction prevents you from slipping when you walk on a sidewalk.

9. True or False: Sliding friction is stronger than static friction.

10. You use _______________ friction when you leave marks on paper with a pencil “lead.”

11. The weakest type of friction that occurs between solid surfaces is ______________ friction.

12. Factors that affect the amount of friction against an object are ___________ and ______________.

13. When you put on the brakes of your bike, the wheels stop turning. Friction between the wheels and the road slows your bike to a stop. Which type of friction is this?

a) fluid friction b) static friction c) sliding friction d) rolling friction 14. The factors that affect gravitational pull on an object are________ and _________________.

15. A) What would you observe if you drop a cotton ball and a rock at the same time? B) Would it be different if you did the same occur if performed in a vacuum tube? Explain your answer.

______________________________________________________________________________

Learning Activity!

Name:___________ No. ____

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Label each of the following images/descriptions below as being examples of 1st, 2nd, or 3rd law.

Then EXPLAIN your answer!

Challenge yourself!

Explanation: 1^st Law 2^nd Law 3^rdLaw ____________________________________________

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