Turbo ScienceTurbo Science

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

Turbo TopicsTurbo Topics

►The following topics will be discussed this The following topics will be discussed this week to give you some information (and week to give you some information (and hopefully enough!) to prevent you from hopefully enough!) to prevent you from freaking out on the CRCT test next week.freaking out on the CRCT test next week.

Disclaimer-Disclaimer- We will be moving at a warp speed this week, so I suggest you give me We will be moving at a warp speed this week, so I suggest you give me

all of your attention.all of your attention. The Big Kahuna (aka Mr. Crawford) has forbidden homework during 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!testing- so I have no way of knowing if you are keeping up with me!

Forcesfrictiongravityspeedvelocityacceleration and Forcesfrictiongravityspeedvelocityacceleration and maybe electricity!maybe electricity!

Forces Forces

► in science it is defined as a push or a pullin science it is defined as a push or a pull►all forces have size and directionall forces have size and direction►measured in newtons (N)measured in newtons (N)►net force- the combination of forces net force- the combination of forces

acting on one objectacting on one object If net force = 0, then the forces are balancedIf net force = 0, then the forces are balanced

and there is no change in motionand there is no change in motion

unbalanced forces- produce a change in unbalanced forces- produce a change in motionmotion

Forces in the same directionForces in the same direction

Forces in different directionsForces in different directions

FrictionFriction

►a force that opposes motiona force that opposes motion►occurs when two surfaces are in occurs when two surfaces are in

contactcontact►amount of friction depends on two amount of friction depends on two

things:things: The force pushing the surfaces together The force pushing the surfaces together

(increases contact)(increases contact) The texture or “roughness” of the The texture or “roughness” of the

surfacessurfaces

Types of FrictionTypes of Friction

kinetic frictionkinetic friction – between moving – between moving objectsobjects

sliding frictionsliding friction – direct and maximum contact – direct and maximum contactex. sliding a box across the floorex. sliding a box across the floor

rolling frictionrolling friction - one object “rolls” over another - one object “rolls” over anotherex. using a cart with wheels to move the boxex. using a cart with wheels to move the box

fluid frictionfluid friction – an object moves through a fluid – an object moves through a fluidex. moving parts of a machineex. moving parts of a machine

Friction: Good or Bad??Friction: Good or Bad??

►Good!Good!- allows us to walk, cars to roll, - allows us to walk, cars to roll, cars to stop and our pencils to writecars to stop and our pencils to write

►Bad!! Bad!! holes in your socks, erosion of holes in your socks, erosion of soil, engine parts wear outsoil, engine parts wear out

We can reduce friction by using We can reduce friction by using lubricants, smoothing the surfaces, lubricants, smoothing the surfaces, using wheels or ball bearingsusing wheels or ball bearings

GravityGravity

►A force of attraction between two A force of attraction between two objects due to their massesobjects due to their masses

►Law of Universal Gravitation-Law of Universal Gravitation- All All objects in the universe exert a objects in the universe exert a gravitational force (pull) on each othergravitational force (pull) on each other The size of the gravitational force The size of the gravitational force

depends on the mass of the objects and depends on the mass of the objects and the distance between themthe distance between them

How Mass affects GravityHow Mass affects Gravity

How Distance affects GravityHow Distance affects Gravity

Weight and GravityWeight and Gravity

►Weight is a measure of the Weight is a measure of the gravitational force on an objectgravitational force on an object

►Weight is measured in newtons (N)Weight is measured in newtons (N)►Weight is related to mass, but it is not Weight is related to mass, but it is not

the same!the same!

A small apple weighs about 1 N

Mass vs. WeightMass vs. Weight

►definitiondefinition►tool used to measuretool used to measure►unitsunits

Make sure you know this!

MotionMotion

►An object is in motion if it changes An object is in motion if it changes position over timeposition over time You must have a reference point!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 MotionMeasuring Motion

SpeedSpeed is the distance an object travels in a is the distance an object travels in a certain amount of timecertain amount of time

S = D/T S = D/T

Example - 60 miles per hour (60 mph)Example - 60 miles per hour (60 mph) 5 meters per second (5 m/s)5 meters per second (5 m/s)

Average speed-Average speed- total distance/total time total distance/total time *because speed is usually not constant*because speed is usually not constant

Try It!Try It!

►Kara jogs to the store 72m away in a Kara jogs to the store 72m away in a time of 36 seconds. What is Kara’s time of 36 seconds. What is Kara’s average speed?average speed?

►An airplane traveling from San Francisco An airplane traveling from San Francisco to Chicago travels 1,260 km in 3.5 to Chicago travels 1,260 km in 3.5 hours. What is the plane’s average hours. What is the plane’s average speed?speed?

Graphing SpeedGraphing Speed

VelocityVelocity

►The speed of an object in a certain The speed of an object in a certain directiondirection

►Velocity must include direction!!Velocity must include direction!!

►Ex. 60 mph eastEx. 60 mph east 5 m/s north 5 m/s north

►Velocity changes if eitherVelocity changes if either speed or direction changesspeed or direction changes

AccelerationAcceleration

►The The raterate at which velocity changes at which velocity changes over timeover time

►Acceleration occurs if:Acceleration occurs if: speed changes speed changes

► speed up- positive accelerationspeed up- positive acceleration► slow down – negative acceleration or slow down – negative acceleration or

decelerationdeceleration

OROR direction changesdirection changes

Yes? or No?Yes? or No?

►You ride your bike around a track at a You ride your bike around a track at a constant speed of 11 km/hconstant speed of 11 km/h

►You ride your bike at 9 km/h and ten You ride your bike at 9 km/h and ten minutes later your speed is 6 km/hminutes later your speed is 6 km/h

►You pedal faster to pass another You pedal faster to pass another bicyclist in the racebicyclist in the race

►You ride your bike in a straight line at You ride your bike in a straight line at a constant speed of 10 km/ha constant speed of 10 km/h

►Acceleration is how quickly velocity Acceleration is how quickly velocity changeschanges

This biker is accelerating at 1 m/s2

For each second that passes, he speeds up by 1 m/s

Try It!Try It!

► An eagle accelerates from 15 m/s to 22 m/s in An eagle accelerates from 15 m/s to 22 m/s in 4 seconds. What is the eagle’s average 4 seconds. What is the eagle’s average acceleration?acceleration?

► A car advertisement states that a certain car A car advertisement states that a certain car can accelerate from rest to 90 km/h in 9 can accelerate from rest to 90 km/h in 9 seconds. What is the car’s average seconds. What is the car’s average acceleration?acceleration?

Graphing AccelerationGraphing Acceleration

Acceleration due to GravityAcceleration due to Gravity

►Objects fall due to gravityObjects fall due to gravity

If you drop a baseball and a ping pong If you drop a baseball and a ping pong ball at the same time, which will hit ball at the same time, which will hit the ground first?the ground first?

►Aristotle said the baseball would.Aristotle said the baseball would.►Galileo proved him wrong!Galileo proved him wrong!

►Acceleration depends on the mass of an Acceleration depends on the mass of an object and the force (gravity) acting on object and the force (gravity) acting on it.it. There is a trade-off between mass and forceThere is a trade-off between mass and force The extra mass of the baseball balances the The extra mass of the baseball balances the

additional gravitational pull needed to additional gravitational pull needed to accelerate the ball.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/s2

All objects accelerate toward

Earth at this rate- for every

second an object falls, it’s

velocity increases by 9.8 m/sThe balls move faster and travel farther in each second than it did in the second before.

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

►The apple will hit first!The apple will hit first!►The feather has more The feather has more air resistance-air resistance- a a

force that opposes the motion of objects force that opposes the motion of objects in air.in air.

There is more surface area on a feather that There is more surface area on a feather that will create friction with the air moleculeswill create friction with the air molecules

This is why we like to have a parachute This is why we like to have a parachute that opens when we jump out of the plane!that opens when we jump out of the plane!

►As the speed of an object increases, As the speed of an object increases, the air resistance increases.the air resistance increases.

►Eventually air resistance (upward Eventually air resistance (upward force) will equal the force of gravity force) will equal the force of gravity (downward force)(downward force)

►Acceleration stops at Acceleration stops at terminal velocityterminal velocity►From then on, the object falls at a From then on, the object falls at a

constant velocityconstant velocity

What if there is no air What if there is no air resistance?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 FallFree Fall

►Occurs when there is no other force Occurs when there is no other force acting on a falling object except acting on a falling object except gravitygravity

►Free fall can only occur where there is Free fall can only occur where there is no air (outer space or a vacuum)no air (outer space or a vacuum)