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# Force and Laws of Motion PowerPoint PPT Presentation

Unit 3 Lesson 7. Force and Laws of Motion. S.8.C.3.1.1,2. The physics classroom website. Force. 1 N= 0.225lbs. A push or pull on an object. Can change the motion of an object Measured in Newtons (N) (kg*m/s 2 ) Friction and gravity are examples. Friction

Force and Laws of Motion

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Unit 3

Lesson 7

## Force and Laws of Motion

S.8.C.3.1.1,2

The physics classroom website

### Force

1 N= 0.225lbs

• A push or pull on an object.

• Can change the motion of an object

• Measured in Newtons (N) (kg*m/s2)

• Friction and gravity are examples.

• Friction

• A force that acts against motion.

• Between objects that are touching

• Between the legs of a desk and the floor when you push a desk

### Gravity

• A force that pulls matter together

• Between objects that are not touching

• Isaac Newton

• “the force of gravity acts between all objects in the universe”

• Gravity exists between all matter

• Gravity exists between you and your pencil however it is very weak

• The more mass an object has, the stronger its gravity

• Keeps objects in orbit around a star, planet or moon.

• Makes objects “fall”

### Combining Forces

Force Diagrams:

• We use arrows to show the different forces acting on objects

• Direction of arrow shows the direction the force is acting

• Length of the arrow shows the strength (size or magnitude) of the force

• Net force: the combination of all forces acting on an object

5N

=

= 10N

5N

5N

10N

=

5N

5N

5N

=

0 N

### Balanced Forces

• When two forces are the same strength (magnitude or size) but acting in opposite directions on a the same object.

• Cannotchange an objects motion (speed and direction)

• An object at rest to start with balanced forces will continueat rest

• An object moving at 30 mph to the left with balanced forces acting on it will continue to move at 30 mph to the left

• Forces are equal

• Motion remains the same

• If not moving, it continues to not move

• If moving , it continues to move exactly the same

Balanced Forces

Forces on the person are balanced: Gravity pulls down on person, chair pushes up on person

10 N

10 N

### Unbalanced Forces

• Will change an objects motion (speed and direction)

• A net force results.

• Net force is calculated by adding forces in the same direction or subtracting forces in opposite directions

• If an object is starting at restwhen a net force of 40 N  is applied, the object will move to the right

• If an object is already moving to the right at a constant speed when a net forceof 40 N  is applied, the object will speed up.

• Net force of 40 N to the Right

• 40 N

• New motion depends on the starting motion

### Newton’s 1st Law of Motion

Law of Inertia

• Object at rest will remain at rest

• Object in motion will continue in motion in a straight line

• The tendency of an object to resist a change in motion.

• The higher the mass of an object , the higher its inertia is.

Unless an unbalanced force acts upon it

Circular motion animation

car making a sharp turn

### Inertia

Video Clip

Bill Nye- Inertia

### Newton’s 2nd Law of Motion

• F = MA

• The larger the net force on an object , the more the objects motion will change (greater acceleration).

• Objects with larger masses, need more force to change their motion.

Newton’s 2nd Law of Motion

### Newton’s 3rd Law of Motion

• When one object exerts a force on another object, the second object exerts an equal but opposite force on the first object

• They are not balanced forces because the forces act on different objects

100 N

100 N

### Newton’s 3rd Law

• Action-Reaction

• For every action (force), there is an equal but opposite reaction (force)

3 laws Video clip

Newton’s 3 Laws