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Newton's 1st Law

Lecture Slides are screen-captured images of important points in the lecture. Students can download and print out these lecture slide images to do practice problems as well as take notes while watching the lecture.

• Intro 0:00
• Question 1 0:15
• Question 2 1:02
• Question 3 1:50
• Question 4 2:04
• Question 5 2:26
• Question 6 2:54
• Question 7 3:11
• Question 8 3:29
• Question 9 3:47
• Question 10 4:02

Transcription: Newton's 1st Law

Hi everyone and welcome back to Educator.com.0000

I am Dan Fullerton and in today's mini-lesson we are going to go through the first page of the APlusPhysics worksheet on Newton's First Law and you can find the link to download that down below the video here.0002

Let us dive right in.0013

Number 1 -- As shown in the diagram, an open box and its contents have a combined mass of 5 kg.0015

A horizontal force of 15 N is required to push the box at a constant speed -- anytime I see that, right away I think acceleration = 0 -- of 1.5 m/s across a level surface.0022

The inertia of the box and its contents increase if there is an increase in the...?0034

Well if we want its inertia to increase -- well, inertia and mass are almost synonymous.0040

Mass is a measure of an object's inertia, so really what we are looking for is an increase in mass, so the correct answer there must be Number 2 -- we will get an increase of inertia if we have an increase in the mass of the contents of the box.0046

Number 2 -- Which unit is equivalent to a Newton per kilogram?0062

Well a Newton per kilogram -- here is how I would do a problem like this.0066

I do not know what that is equal to, but I know Newton's measure force and force is equal to mass times acceleration.0071

So I am going to say that Newton is equal to the units of mass times the units of acceleration, so a Newton must be equal to the units of mass, a kilogram, and acceleration, a meter per second squared.0078

A Newton per kilogram would be a kg-m/s2 and I have to divide the kilogram, which will make a ratio of 1 and I am left with a meter per second squared, so Answer Number 1.0091

Number 3 -- Which of these objects have the most inertia? Again, inertia/mass, they are the same thing.0110

In this case the one with the most mass is Number 4, a 10 kg sled at rest.0118

Number 4 -- If the sum of all the forces acting on a moving object is 0 -- that means the net force is 0 -- the object will...?0124

Well, with Newton's First Law says if there is no net force on an object it is going to continue at a constant velocity, so the answer is Number 4, it is going to keep doing what it is doing.0134

Number 5 -- The mass of a high school football player is approximately...?0145

Mass is a measure of an objects inertia, but the mass of a high school football player -- more of an idea if you can estimate metric units, so that is going to be about 100 kg on the order of 200 and a little bit more pounds for those who are more familiar with pounds.0150

About 100 kg is a pretty big, solid person.0168

Number 6 -- Which object has the greatest inertia?0173

Again, if you do not like the word inertia, write mass in there, so the answer is Number 4, the only one that has the most mass at 20 kg.0176

All of this stuff about how fast they are moving does not make a difference.0187

Number 7 -- I have a data table that lists the mass and speed of four different objects. Which object has the greatest inertia?0192

Same deal, again we are looking for the one that has the greatest mass.0198

There it is, so it must be object (D), so the correct answer is Number 4.0203

Number 8 -- A half kilogram cart is rolling at a speed of 0.4 m/s. If the speed of the cart is doubled, the inertia of the cart will...?0209

Again, what is going to happen to the carts mass if you double the speed? Nothing, it is going to remain unchanged.0218

Number 9 -- Which person has the greatest inertia? Again, if you do not like the word inertia, write mass in there and by far the biggest mass is going to be the 110 kg wrestler -- that is a solid wrestler.0228

Finally, Number 10 -- Which object has the greatest inertia? A fallen leaf, a soft ball, a high school student, or a helium-filled toy balloon?0242

Again, if you do not like the word inertia, think of mass.0252

By far the most mass out of those choices, is the seated high school student, who has a mass of around 60, 70 kg, probably a typical high school student.0256

That concludes page 1 of our worksheet on Newton's First Law.0266

Thanks so much for your time and make it a great day everyone!0272