FRICTION J Willis CMS Friction Rub your hands

FRICTION J. Willis CMS

Friction Rub your hands together What do you notice?

Friction • Force when two surfaces rub together • Strength of the friction depends on… – 1) how hard the surfaces push together – 2) the type of surface (rough or slick)

• Friction force acts in a direction opposite to the motion. • There is very little friction between the snow and the skis. The snow is icy and slick as the skis glide overtop.

All surfaces have a texture. This is a piece of paper under a microscope. What we think is smooth, is really very bumpy.

Types of friction 1) static – acting on an object that is not moving 2) sliding – two solids slide over each other 3) Rolling – objects roll across a surface 4) Fluid – solid in a fluid (air or water)

• Reduce friction by adding oil between parts of a machine. • Parts will float in the fluid and not touch directly.

Gravity • The force that pulls ALL objects together • All objects exert a gravitational pull upon each other.

Universal Law of Gravitation The force of gravity acts between all objects in the universe.

Two things affect gravity 1) Mass ---- amount of matter in an object 2) Distance --- how far objects are from one another

A lot of Mass = A lot of gravitational pull Not much Mass = Not much gravitational pull

Closer together = More gravitational pull Further apart = Less gravitational pull

Weight • Weight is the measure of the force of gravity on an object. • Weight is NOT the same as Mass • Weight can change if the amount of gravitational pull changes • Weight is usually measured in Newtons. http: //www. exploratorium. edu/ronh/weight/

Free Fall is when the only force on an object is gravity. 1) In a free fall everything falls at the same rate regardless of its mass! http: //www. youtube. com/watch? v=4 m. Tsr. RZEMw. A&feature=related http: //www. redbullstratos. com/the-mission/world-recordjump/#!lightbox[sidepods]/media 1902415096001 -2100/

Acceleration of Gravity • Near Earth, any object accelerates at a rate of 9. 8 m/s 2 ----- Regardless of Mass! 9. 8 m/s 2

Air Resistance 1) type of fluid friction 2) it slows motion 3) it is not the same for all objects ex. Leaf vs. Acorn

Terminal Velocity • The greatest velocity a falling object can reach. • 122 mph - normal • 200 mph – pull in arms and legs • 843. 6 mph – world record (Baumgartner)

Projectile - thrown or projected with force • A thrown object will hit the ground at the same time a dropped object hits the ground. • If they are dropped/thrown from the same height and have NO Air Resistance http: //www. youtube. com/watch? v=D 9 w. QVIEd. Kh 8

Two Forces Slows motion Strength 4 types are… depends on… Pulls objects closer 2 factors that When it’s the affect it are… only force, objects Slowed down by Will still affect thrown objects

Two Forces GRAVITY FRICTION Slows motion Strength 4 types are… depends on… TYPE OF SURFACE HOW HARD THE SURFACES PUSH TOGETHER Pulls objects closer 2 factors that When it’s the affect it are… only force, objects STATIC MASS SLIDING DISTANCE ROLLING FLUID FREE FALL Can slow by AIR RESISTANCE Will still affect thrown objects PROJECTILE

WB pages 139 -142