Tuesday January 31st Friction, Air Resistance, And Terminal Velocity!

What will we learn today? Content Objectives: Students will be able to compare amounts of friction in different scenarios Literacy Objective: Students will be able to define friction as the force that opposes the motion of two surfaces that are in contact

Yesterday… …we talked about forces, free-body diagrams, and balanced/unbalanced forces. And one student (Gabe) brought up an interesting idea… …if we drag this block across the table… isn’t there friction that slows it down?? So don’t we need to add that to our free-body diagram?

Friction Friction is the force that opposes the motion of two surfaces that are in contact The size of the frictional force depends on: – The materials the surfaces are made from (how rough they are) – The force pushing the two surfaces together (more force = more friction!)

A Closer Look at Friction

Three Types of Friction Static Friction: frictional force that prevents two surfaces in contact from sliding past each other – (there is no movement! The objects are static, defined as “fixed or stationary”) Man’s force Frictional force Balanced Forces means NO MOVEMENT

Static Friction Static Friction increases as the downward force increases More downward force = more contact between the two rough surfaces = more friction. Let’s test it out!

Three Types of Friction Sliding Friction: frictional force that acts in the opposite direction to the motion of a surface sliding on another surface This time, there IS movement Smaller than force due to Static Friction Unbalanced Forces means A CHANGE in velocity = movement! Man’s force Frictional force

Three types of Friction Rolling Friction: frictional force that acts in the opposite direction to the motion of a surface ROLLING over another surface Smallest frictional force (of the three type)

Let’s take a look at how POWERFUL friction can be… LY LY JE JE

Friction lets us… Walk on the ground without slipping! Rock Climb! Stop a moving car! Hold a Pencil Wear Glasses or sunglasses without them falling off

A Special Type of Friction Air Resistance is a type of friction that opposes the motion of objects that move through the air Without Air Resistance, all objects would fall at the same rate of speed Parachutes significantly increase air resistance, allowing for a safe landing for skydivers!

Skydivers Reach a terminal velocity of 120 mph when laying “flat” and mph when diving head-first Terminal Velocity is when air resistance equals the accelerating force of gravity and the object cannot go any faster. After the parachute is deployed, air resistance significantly increases and skydivers decelerate to a rate of 18mph

Lets see Air Resistance in Action: WIU WIU Balanced Forces: r0 r0