Chapter 10 force and motion STUDY GUIDE/NOTES FRICTION GRAVITY NEWTON’S LAWS OF MOTION

What is Friction? The force that 2 surfaces exert on each other when they rub against each other. Types of Friction Static friction Sliding friction Rolling friction Fluid friction

What are the Causes of Friction? The strength of the force of friction depends on two factors: how hard the surfaces push together and the types of surfaces involved. Smooth surfaces have less friction; bumpy surfaces have more Friction acts in a direction opposite to the direction of the object’s motion

What is Static Friction? Friction that acts on objects that are not moving Because of static friction, you must use more force to start the motion of stationary objects Once you start an object moving there is no longer static friction

What is Sliding Friction Occurs when 2 solid surfaces slide over each other Examples: spreading sand on icy path Ballet dancers applying resin to ballet slippers so they don’t slip Bicycle brakes Skinning your knee

What is Rolling Friction Occurs when an object rolls across a surface Easier to overcome than sliding friction for similar materials Ball bearings are in moving objects such as skates, skateboards, and bicycles Ball bearings reduce friction by rolling between moving parts

What is Fluid Friction Occurs when solid objects move through a fluid like a gas(air) or liquid Easier to overcome than sliding friction Reason why moving parts are often bathed in oil or other lubricants Fluid friction occurs between a bicyclist and the air. Bicyclists often wear streamlined helmets and clothes

How can we reduce the friction between 2 objects? Reduce the contact area by using rollers/ball-bearings/wheels Change the surfaces of the materials that are touching by using lubrication ex. Oil Create a cushion of air EXAMPLE. Like a hovercraft or air hockey table

Low friction Ski’s on the snow WATER ON A SLIDE

High friction Brakes on a bike PENCIL AND ERASER CAR TIRE

FACTORS THAT AFFECT FRICTION SURFACE AREA- HOW MUCH CONTACT BETWEEN THE 2 SURFACES RUBBING TOGETHER- MORE CONTACT WITH SURFACE , MORE FRICTION TEXTURE- ROUGHER SURFACES CREATE MORE FRICTION THAN SMOOTHER SURFACES MASS/WEIGHT- LARGER OBJECTS CREATE MORE FRICTION THAN SMALLER ONES. LARGER OJBECTS ARE HARDER TO MOVE.

What is a force? A force is a push or pull that causes an object to move, stop, or change direction In physics a force is anything that makes an object accelerate

Force Forces come in pairs Forces have a magnitude and a direction Magnitude: 5N Direction: north (up) 5N, north (up)

Balanced and Unbalanced Forces Forces occur in pairs and they can be either balanced or unbalanced

Balanced Forces Balanced forces do not cause change in motion They are equal in size and opposite in direction

Some Examples from Real Life A soccer ball is sitting at rest. It takes an unbalanced force of a kick to change its motion. Two teams are playing tug of war. They are both exerting equal force on the rope in opposite directions. This balanced force results in no change of motion.

Unbalanced Forces An unbalanced force always causes a change in motion When unbalanced forces act in opposite directions you can find the net force Net force Magnitude The difference between the two forces Direction Direction of the largest force

Unbalanced Forces 3 N, right – 6 N, left = 3N, left

Unbalanced Forces 4 N, left – 10 N, right = 6N, right

Unbalanced Forces 5 N, right + 10 N, right = 15N, right