Set your stuff down, get ready to go to the media center for first part of class

WHAT IS A FORCE?.

Force- Definition A push or pull in a direction

Characteristics of Forces Forces are measured in Newtons (N) Forces are measured in Newtons (N) They usually work in pairs They usually work in pairs Have a direction Have a direction Affect motion Affect motion

Types of Forces Gravity Gravity Friction Friction Magnetic Magnetic Elastic Elastic Applied Force Applied Force

How do Forces act on Objects? Force Diagrams gravity friction Normal force (force of ground/Earth)

Force Diagrams “free fall” gravity friction (air resistance)

Force Diagram gravity friction Normal force (force of slide/Earth)

Force Diagrams gravity friction Normal force (force of ground/Earth) Applied (guy pushing)

Net Force Net Force = The sum of all the forces on an object Same direction, add Same direction, add 20+10=30N 20+10=30N Opposite direction, subtract (bigger one wins) Opposite direction, subtract (bigger one wins) 20-10= 10N 20-10= 10N

STOPPED HERE ON FEB 11

Newton’s Laws of Motion I. Law of Inertia II. F=ma III. Action-Reaction

While some people know what Newton's laws say, many people do not know what they mean (or simply do not believe what they mean). Newton’s 3 Laws of Motion

1 st Law of Motion (Law of Inertia) Objects will stay at rest, or stay in motion until an outside force acts on it.

1 st Law Inertia the tendency of an object to resist changes in motion Inertia the tendency of an object to resist changes in motion The more mass, the more inertia something has

1 st Law Unless acted upon by an unbalanced force, this golf ball would sit on the tee forever. Unless acted upon by an unbalanced force, this golf ball would sit on the tee forever.

1 st Law Once flying in the air, if an unbalanced force wasn't applied (such as gravity or air friction), it would never stop! Once flying in the air, if an unbalanced force wasn't applied (such as gravity or air friction), it would never stop!

Question Why then, do we observe every day objects in motion slowing down and becoming motionless seemingly without an outside force?

FRICTION!! Objects on earth, are under the influence of friction. (friction from the air, friction when rolling on a surface, friction when sliding)

Newtons’s 1 st Law and You Don’t let this be you. Wear seat belts! Because of inertia, objects (including you) resist changes in their motion. When the car going 80 km/hour is stopped by the brick wall, your body keeps moving at 80 m/hour.

Newton's 2 nd Law

2 nd Law The net force of an object is equal to the product of its mass and acceleration, or F=ma. Force = Mass x Acceleration

Newton's 3 rd Law For every action, there is an equal and opposite reaction. For every action, there is an equal and opposite reaction. When you sit in your chair, your body exerts a downward force on the chair and the chair exerts an upward force on your body.

3 rd Law Birds depend on Newton’s third law of motion. As the birds push down on the air with their wings, the air pushes their wings up and gives them lift.

3 rd Law 3 rd Law Think of a car moving forward..... Think of a car moving forward..... Which direction do the wheels move against the road in the picture below?? Which direction do the wheels move against the road in the picture below?? Car moving this way