FORCES Lesson 1 Friction and Gravity

What is a Force? (p.44) A push or a pull on an object in a particular direction.

CONTACT FORCES (P.44) Does not require contact: NON-CONTACT FORCES (P.46) Force through CONTACT: *Virtually all actions require a… Magnetic: Static: Gravity: Forces are measured in NEWTONS

GRAVITY (P.47) An attractive force that exists between all objects that have mass. This force is dependent on mass and distance from the object.

WEIGHT VS MASS (P. 48) What is the difference? Weight: Is the gravitational force exerted on an object. Your weight is actually a force measured in Newton’s. Mass: Amount of matter in an object. Demonstration: Mass & Gravity LINK

GRAVITY AND AIR RESISTANCE Most objects falling through air experience a type of fluid friction called air resistance. Air resistance is not the same for all objects. The greater the surface area of the object the greater the air resistance. (paper drop) However, since the elephant has more mass, it has more downward force of gravity and falls faster.

GRAVITY AND FREE FALL An object is in free fall when the only force acting on the object is gravity. Free-falling objects do not encounter air resistance. In free fall, the force of gravity is an unbalanced force. Gravity Tube Demonstration Take away ALL air, so that only the force of Gravity is being used. TRY THIS

CALCULATING FREE FALL All objects in free fall accelerate at the same rate – 9.8 m/s² - regardless of their mass. in one second = 9.8 m/s² in two seconds = 19.6 m/s² in three seconds = 29.4 m/s² in four seconds = ________ The velocity continues to increase as the object falls.

UNIVERSAL GRAVITATION The law of universal gravitation states that the force of gravity acts between all objects in the universe. (1:47 min)

WHAT IS FRICTION? (P.49) Friction is a force that resists the motion of two surfaces that are touching. When a moving object comes in contact with another object, friction is the opposing force that slows or stops the moving object. *Static.. prevents objects sliding *Sliding... resists objects while they are moving *Fluid… air or water

Without friction, an object would continue to move at constant speed forever. The strength of the force of friction depends on the type of surfaces and how hard the surfaces push together. Rough surfaces produce greater friction than smooth surfaces. TRY THIS

When FRICTION just isn’t there

SLIDING FRICTION A resistance to movement that is created when two things rub together.

WAYS TO REDUCE FRICTION Smooth the surface / Put ball bearings in wheels Replace rolling with sliding / Add oil or another type of lubricant (5:41 min) Friction In Daily Life

A WORLD WITHOUT FRICTION (2:41 MIN)

FLUID FRICTION The force that tries to slow objects down when they move through a liquid or a gas. It's also known as "drag", or "air resistance". All gases and liquids are fluids. An airplane and a swimmer both experience fluid friction.