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# AP Physics 1 review of 1D motion

In this video David rapidly explains all the concepts in 1D motion and also quickly solves a sample problem for each concept. Keep an eye on the side scroll see how far along you've made it in the review video. Created by David SantoPietro.

## Want to join the conversation?

• How can I get this document?
• hey what does a negative displacement interpret...what does negative displacement mean...for how could my speed be negative...is it not speed scalar...someone pls help me with the concept
• Displacement is relative, which means that negative displacement will be the opposite of what you define as positive. For example, if walking forward is a positive displacement, then going backwards is a negative displacement. Speed just measures how fast you are going, regardless of direction. Velocity, however, has a direction can be negative(saw my mistake in comments).
• Has anyone taken the exam this year already?
I would love some general concepts to focus on and any tips that could help.
• Hey,
I took the AP Physics 1 Exam this year. My main advice would be to really focus on understanding the theory behind the content (as opposed to just plug/chug) - this conceptual framework behind the exam makes it really different from other physics exams. Other resources include FlippingPhysics, APlusPhysics, and of course this website. Do tons of practice questions to get used to the style of questions on the Exam, which contains a LOT of reading/writing; also use the official AP 1 formula sheet when doing practice problems, so you are prepared for exam day.
Good Luck,
NP
• how would you find the initial velocity for an object released from a height if only the height and distance are given?
• The object is merely released from a height? Why, then, the initial velocity must equal zero! :)
• Will I miss something if I skip the lectures from 1D motion to Quantum Physics? By just watching all these review videos?
• Why is acceleration velocity over time and not distance over time?
• By definition.
velocity is rate of change of displacement.
Acceleration is rate of change of velocity.
• I have a book about physics that I use to study. It doesn't explain it the same way as David SantoPietro. Can anyone recommend a book to use that explains 1D motion the same way as him? Also, does Kahn Academy have textbooks, so when I travel on a plane, I can do Kahn Academy at that time?
• While I can't recommend you to a textbook that teaches similarly to David, I can tell you that a digital textbook company called Kno is integrating Khan Academy into their etextbooks. That's probably your best bet.
• At how did you get 4 meters every 2 seconds instead of 2 meters every 2 seconds? On the example problem, there are arrows explaining how every two seconds 4 meters has passed, but can you explain why it is 4 meters and not 2?
• So the time on the x axis is shown in increments of 2 seconds right? And the graph shows that every 2 seconds the curve travels 4 meters since that is the max height (amplitude of the graph). Therefore, since the curve always travels 4 meters every two seconds (regardless of direction), it must travel 2 meters every second and therefore the average speed is 2 meters per second.
• Under the section "Freely Falling Object," how is the answer t = radical 2h / g? I don't understand how that answer was gotten to.
• The equation x=x0+v0t+1/2at^2.
x0=0 and v0=0, so you are left with x=(1/2)at^2.
The distance the textbook has fallen is H, so x=-H. Your equation is now -H=(1/2)at^2.

When you have a free falling object, the acceleration is always -9.8m/s^2 (gravity). If g=9.8m/s^2, you can substitute -g in for 'a' to get -H=(1/2)(-g)t^2.

Then you solve for time.
The negatives on both sides of the equation cancel out => H=(1/2)gt^2
Multiply both sides by 2 => 2H=gt^2
Divide both sides by g => 2H/g=t^2
Then square root both sides, and you should have the answer!