Chapter 3 Motion in a line (linear motion)

Motion Vocabulary A cat moves a distance of 10 meters (how far?) in 5 seconds. What information do you KNOW from this? What can you calculate? ______(technically ____________) = ______ –Most common units: _______________________ ____________– speed _________________ –This is the quantity scientists use. _______tells us how ___________________________________ _______________.

Speed/velocity questions Questions: a car moves 20 meters/sec. How far does it go in: –3 seconds? _______________ –10 seconds? _______________ –1 minute? _______________ –1 hour? _______________ Describe how something could move with constant speed but CHANGING velocity.

When you’re sitting completely still, are you moving? 1.Yes 2.No

Debrief Talk to your neighbors: –Did you get it right? –Why or why not? –Make sure you understand.

Motions Daily motion – Earth’s rotation once per __ –Speed varies: ___ for Santa, __________for __________ ______________________________ Yearly motion – Earth’s revolution once per __ –Distance: 1AU = ____ –Speed: average ~_______________mph –Direction _______________________________. Sun _______________________________ -230 Million yr –28,000 light-year radius, speed ~500,000 mph –Studying this motion  _________________________ Galaxies moving relative to each other. –________________________________________________.

Acceleration Acceleration – any change in velocity –___________________________________ –__________________________________ In everyday English, slowing down is called “________” but physicists use “accelerating” to mean _________________________________. Give some examples of things that are “accelerating” in the physics sense.

Velocity vs. acceleration Identify the following as velocity (arm points right) or acceleration (arm points left) –Going 55 mph –Using the gas pedal on your car –Rolling in a straight line –Using the brakes on your car –Using the steering wheel on your car –Running 10 meters per second –Things falling due to gravity. –Things thrown upwards on their way up to the top

Which does the human body feel? Velocity 2.Acceleration

Debrief Talk to your neighbors: –Did you get it right? –Why or why not? –Make sure you understand. ** For this question, the same is true for ___________. They FEEL ___________.

Accelerating – changing velocity When things ____________________ ____________ in a _______________ way –Cars go from zero to ____ in ____ seconds. –That’s an acceleration of _______________ –Sprinters run at a top speed of _________ meters/sec (or _____mph). –How long does it take to speed up? (Or slow down?) –Calculate the accelerations.

Airplanes travel at a constant speed of 400 miles/hr. Is the airplane accelerating? Yes 2.No 3.Not enough information provided

Debrief Talk to your neighbors: –Did you get it right? –Why or why not? –Make sure you understand.

Two track demo See page 57, question 40. Clicker question coming: –Which reaches end of track first?

Which ball reaches the end of the track first? Same time 2.Ball on a straight path 3.Ball on the downhill/uphill path

Debrief Talk to your neighbors: –Did you get it right? –Why or why not? –Make sure you understand.

Acceleration changing an object’s speed Ramp demo Imagine something accelerates at a constant rate of 2 miles/hr per second of motion. It starts at rest. Work with your neighbor. –Initially, its speed is _____________ –After 1 second, its speed is ____________ –After 2 second, its speed is ____________ –After 3 second, its speed is ____________ –After 10 secs, its speed is ____________ –After 2000 secs, its speed is ____________ –Write a rule for the speed after “T” seconds. –After you write your rule, notice the textbook gives an equation on page 47.

A super-fast car and truck start at the same place. The car goes 100 m/s (220 miles/hr) always. The truck starts at rest and accelerates 1 m/s per HOUR. Will the truck ever catch the car? Yes 2.No 3.Not enough information is provided

Debrief Talk to your neighbors: –Did you get it right? –Why or why not? –Make sure you understand.

_______________________________ _________ covered more distance? Car 2.Truck 3.Same 4.Not enough information is provided

Debrief Talk to your neighbors: –Did you get it right? –Why or why not? –Make sure you understand.

_______________________________ ______________ is moving faster? Car 2.Truck 3.Same 4.Not enough information is provided

Debrief Talk to your neighbors: –Did you get it right? –Why or why not? –Make sure you understand.

Calif. Science Standards for motion From California Science Standards, grade 2: –Students know the way to change how something is moving is by giving it a push or a pull. The size of the change is related to the strength, or the amount of force, of the push or pull. And from grade 8: –Students know the velocity of an object must be described by specifying both the direction and the speed of the object. –Students know changes in velocity may be due to changes in speed, direction, or both.

Gravity near ground Free fall –Toss something up, what happens on way up? –Drop something, what happens on way down? When things fall, measure ________________ for: –_______________ –_______________________________________of falling. Paper/pen experiment _____________________________________for ___ __________________________________________ –*Unless there are __________, such as _____________ –Then we’re dealing with NET force, not gravity’s force. Galileo observed this (in Pisa). Galileo’s observations helped Newton formulate ideas.

From Apollo 15 mission Men on the Moon Show the hammer-feather movie Search internet for this if you want to see it at home.

Gravitational acceleration g = 10 m/s per second or 22 mph per sec Drop something from rest. How fast will it be moving after: –1 sec _______________ –2 sec _______________ –10 sec _______________ –T sec _______________* *After writing your rule, compare yours to the book’s version on p. 48 –10 m/s 2 (on Earth’s surface) is abbreviated “g”** **More precisely it’s 9.8 m/s 2.

Free fall questions What happens to an object if you drop it at rest? –How quickly? If you toss something straight upwards –What happens on the upwards part of motion? How quickly? –What happens on the downward part? How quickly?

How fast is something moving at the top of the motion after being thrown upwards? The answer depends on: Nothing – it is moving w/ speed=zero 2.how fast it was thrown 3.How long you wait 4.how fast thrown & how long you wait

What is the acceleration at the top of the motion after being thrown upwards? Zero 2.g 3.Not enough information provided

You have two spheres of equal size and smoothness, and you can ignore air resistance. One is heavy, the other much lighter. You hold one in each hand at the same height above the ground. You release them at the same time. What will happen? 1.The heavier one will hit the ground first. 2.They will hit the ground at the same time. 3.The lighter one will hit the ground first

Same objects. How does the acceleration of gravity compare? 1.The heavier one has a larger gravitational acceleration. 2.They have the same gravitational acceleration. 3.The lighter one has a larger gravitational acceleration

Same objects. How does the force of gravity compare? Be careful! 1.The heavier one has a stronger gravitational force. 2.They have the same gravitational force. 3.The lighter one has a stronger gravitational force

California Elementary School Science Standards for gravity From California Science Standards, hgih school a.Students know the relationship between the universal law of gravitation and the effect of gravity on an object at the surface of Earth.

Summary 1.Definitions: speed, velocity, acceleration 2.Differences between these three 3.Simple computations of speed & accel. 4.Gravity is an acceleration 5.All things freefall with same acceleration