Turbo Science for the “academically advanced“ (a.k.a. “really smart when they apply themselves” students)

Turbo Topics ► The following topics will be discussed this week to give you some information (and hopefully enough!) to prevent you from freaking out on the CRCT test next week. Disclaimer-  We will be moving at a warp speed this week, so I suggest you give me all of your attention.  The Big Kahuna (aka Mr. Crawford) has forbidden homework during testing- so I have no way of knowing if you are keeping up with me! Forcesfrictiongravityspeedvelocityacceleration and maybe electricity!

Forces ► in science it is defined as a push or a pull ► all forces have size and direction ► measured in newtons (N) ► net force- the combination of forces acting on one object  If net force = 0, then the forces are balanced and there is no change in motion and there is no change in motion unbalanced forces- produce a change in motion

Forces in the same direction

Forces in different directions

Friction ► a force that opposes motion ► occurs when two surfaces are in contact ► amount of friction depends on two things:  The force pushing the surfaces together (increases contact)  The texture or “roughness” of the surfaces

Types of Friction kinetic friction – between moving objects kinetic friction – between moving objects sliding friction – direct and maximum contact ex. sliding a box across the floor rolling friction - one object “rolls” over another ex. using a cart with wheels to move the box fluid friction – an object moves through a fluid ex. moving parts of a machine

Friction: Good or Bad?? ► Good!- allows us to walk, cars to roll, cars to stop and our pencils to write ► Bad!! holes in your socks, erosion of soil, engine parts wear out We can reduce friction by using lubricants, smoothing the surfaces, using wheels or ball bearings

Gravity ► A force of attraction between two objects due to their masses ► Law of Universal Gravitation- All objects in the universe exert a gravitational force (pull) on each other  The size of the gravitational force depends on the mass of the objects and the distance between them

How Mass affects Gravity

How Distance affects Gravity

Weight and Gravity ► Weight is a measure of the gravitational force on an object ► Weight is measured in newtons (N) ► Weight is related to mass, but it is not the same! A small apple weighs about 1 N

Mass vs. Weight ► definition ► tool used to measure ► units Make sure you know this!

Motion ► An object is in motion if it changes position over time  You must have a reference point! We can tell the balloon is in motion because its position has changed with reference to the mountain.

Measuring Motion Speed is the distance an object travels in a certain amount of time S = D/T Example - 60 miles per hour (60 mph) 5 meters per second (5 m/s) 5 meters per second (5 m/s) Average speed- total distance/total time *because speed is usually not constant *because speed is usually not constant

Try It! ► Kara jogs to the store 72m away in a time of 36 seconds. What is Kara’s average speed? ► An airplane traveling from San Francisco to Chicago travels 1,260 km in 3.5 hours. What is the plane’s average speed?

Graphing Speed

Velocity ► The speed of an object in a certain direction ► Velocity must include direction!! ► Ex. 60 mph east 5 m/s north 5 m/s north ► Velocity changes if either speed or direction changes speed or direction changes

Acceleration ► The rate at which velocity changes over time ► Acceleration occurs if:  speed changes ► speed up- positive acceleration ► slow down – negative acceleration or deceleration OR  direction changes

Yes? or No? ► You ride your bike around a track at a constant speed of 11 km/h ► You ride your bike at 9 km/h and ten minutes later your speed is 6 km/h ► You pedal faster to pass another bicyclist in the race ► You ride your bike in a straight line at a constant speed of 10 km/h

► Acceleration is how quickly velocity changes This biker is accelerating at 1 m/s 2 For each second that passes, he speeds up by 1 m/s

Try It! ► An eagle accelerates from 15 m/s to 22 m/s in 4 seconds. What is the eagle’s average acceleration? ► A car advertisement states that a certain car can accelerate from rest to 90 km/h in 9 seconds. What is the car’s average acceleration?

Graphing Acceleration

Acceleration due to Gravity ► Objects fall due to gravity If you drop a baseball and a ping pong ball at the same time, which will hit the ground first?

► Aristotle said the baseball would. ► Galileo proved him wrong! ► Acceleration depends on the mass of an object and the force (gravity) acting on it.  There is a trade-off between mass and force The extra mass of the baseball balances the additional gravitational pull needed to accelerate the ball. The extra mass of the baseball balances the additional gravitational pull needed to accelerate the ball.

This stop action photo shows that a ping pong ball and a golf ball fall at the same rate even though they have different masses. Acceleration due to gravity is 9.8 m/s 2 All objects accelerate toward Earth at this rate- for every second an object falls, it’s velocity increases by 9.8 m/s The balls move faster and travel farther in each second than it did in the second before.

► If a feather and an apple are dropped from the same height at the same time, which will hit the ground first?

► The apple will hit first! ► The feather has more air resistance- a force that opposes the motion of objects in air.  There is more surface area on a feather that will create friction with the air molecules This is why we like to have a parachute that opens when we jump out of the plane!

► As the speed of an object increases, the air resistance increases. ► Eventually air resistance (upward force) will equal the force of gravity (downward force) ► Acceleration stops at terminal velocity ► From then on, the object falls at a constant velocity

What if there is no air resistance? In a vacuum, a feather and an apple will fall at the same rate The only force acting on the object is gravity - free fall

Free Fall ► Occurs when there is no other force acting on a falling object except gravity ► Free fall can only occur where there is no air (outer space or a vacuum)