What is F=ma: Definition and 192 Discussions

In classical mechanics, Newton's laws of motion are three laws that describe the relationship between the motion of an object and the forces acting on it. The first law states that an object either remains at rest or continues to move at a constant velocity, unless it is acted upon by an external force. The second law states that the rate of change of momentum of an object is directly proportional to the force applied, or, for an object with constant mass, that the net force on an object is equal to the mass of that object multiplied by the acceleration. The third law states that when one object exerts a force on a second object, that second object exerts a force that is equal in magnitude and opposite in direction on the first object.
The three laws of motion were first compiled by Isaac Newton in his Philosophiæ Naturalis Principia Mathematica (Mathematical Principles of Natural Philosophy), first published in 1687. Newton used them to explain and investigate the motion of many physical objects and systems, which laid the foundation for Newtonian mechanics.

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  1. P

    F=ma problem, I feel retarded because I can't get it

    Seriously I feel so stupid because I can't get the answer to the second part of the problem, what am I doing wrong? Homework Statement 2 parts to the problem: An empty truck whose mass is 1500 kg has a maximum acceleration of 1.4 m/s^2 . What is the maximum force that accelerates the...
  2. M

    Solving 2007 F=ma Physics Olympiad Problems: AP Phys. C Study Guide

    I'm going through the 2007 Physics Olympiad F=ma test tonight (first 27 questions). It's available http://www.aapt.org/Contests/upload/olympiad_2007_fnet_ma.pdf" , if you're wondering. I'll post my attempts here as I get to them. Tell me what I'm doing right or wrong. I don't really know this...
  3. K

    2008 F=ma Olympiad Problems # 10 + 11

    These two problems are based one some data from an experiment. Of course, experiment often don't carry out perfectly matching theory... And I'm having some difficulty understanding the answer. Problem: The following information applies to the next two problems An experiment consists of...
  4. R

    F=ma calculation in vector format

    I am given F=(3i + 2j + 4k) N and mass = 2kg I need to calculate acceleration, so I plugged it into F=ma, am I right in saying (3i + 2j + 4k) = 2 a \frac{(3i + 2j + 4k)}{2} = a therefore a = 1.5i + 1j + 2k ? cheers.
  5. M

    Has anyone done 2008 F=ma contest?

    I've been practicing for 2009 F=ma contest (Physics Olympiad preliminary test) by doing 2008 test but the last 10 problems are TOUGH I couldn't solve any of them correctly Can anyone help me with them?
  6. T

    Does Bouyant Force Affect Scale Readings?

    Homework Statement Before you submerge a block (25N) in water, you place the container of water on a scale. The scale reads 100N. You then immerse the block in the water, the block is also hung on a scale that reads 17N. Is the scale reading greater than, less than, or equal to 100N? (...
  7. R

    Applying Newton's Laws (Inertia, F=ma, Action Reaction_

    Hey guys, This is my first time using these forums, so forgive me if I do/post anything wrong! Anyways, I need help on a question...and this might be on a physics test I'm having tommorow. I'm not that great in physics, so I need a bit of help. If anyone can tell me their opinion, please do so...
  8. U

    What Happens to the Acceleration When the Thread Snaps?

    Homework Statement A mass of 1kg is suspended from a 50N spring balance, and then a thread from the first mass suspends a further mass of 2kg. The thread is then burned through. What is the acceleration of each mass at the instant the thread snaps? Homework Equations F=ma The Attempt at...
  9. C

    Solve F=ma Pulley Problem: Mass of Sand & Acceleration

    1. A 28.0 kg block is connected to an empty 1.35 kg bucket by a cord running over a frictionless pulley. The coefficient of static friction between the table and the block is 0.450 and the coefficient of kinetic friction between the table and the block is 0.320. Sand is gradually added to the...
  10. R

    Light Speed and Newton's Equation F=ma: Explanation

    Im just an amateur, and I read that Newton's Equation F=ma doesn't work when approaching light speeds because of a relative increase in mass at higher velocicites. What is the reason for this, if any, and is there a ratio between veolcity and relative mass I could use to make my calculations...
  11. V

    Understanding Newton's Second Law: Deriving the Equation F=ma

    I knew i should have paid more attention in class =/ anyways, We have been studying Newton's second law. And I have a question on my lab that asks for me to "derive equation for a (acceleration) vs F (force) and a (acceleration) vs m (mass)" a vs F and a vs M are two graphs which we did...
  12. J

    How Does Elevator Acceleration Affect Object Weight?

    1. Question A lift has a object of mass 5kg inside. Find the reaction force of the lift upon the object, and the object's relative weight when: The lift is descending with an acceleration of 3m/s The lift is descending with constant speed The lift is decelerating at a rate if 3m/s (while...
  13. Y

    How did Newton come about with F=ma?

    If he's thought Force must be proportional to the mass and acceleration why didn't he write down the equation in: F=kma form , how did he cancel out the k constant? or did he come to the solution with Galileo's fallen objects experiments and reasoned : a=F/m (a equals to g here of...
  14. B

    How to find the tension using the F=ma formula

    A 4.0 kg and 6.0 kg masses are connected by a string over a pulley. What is the tension in the String? I have no idea how to find the tension using the F=ma formula Can someone please help me? Please also explain tension in terms of the word meaning in Physics. Thank you very much!
  15. U

    Solve Physics F=ma Help Problem

    Physics F=ma Help! Homework Statement Ok so I'm supposed to present the solution of a problem to my AP Physics class tomorrow. The thing is, I don't understand the question at all! Here is the problem (easy) and the possible answer choices. How would I go about doing this? A 150-N sled...
  16. O

    Calculating Acceleration: Basic Question on F=ma in AP Physics

    I know this is rather basic, but some how I confused myself... The question is: An astronaut of mass 75 kg performs repair work on the 1700 kg satellite, while floating right next to it. He exerts a force of 180 N on the satellite. What is his acceleration as a consequence of this, and what...
  17. P

    F=ma prob with electrons (They don't even act like particles )

    F=ma prob with electrons (They don't even act like particles!) Well here's the problem: 1. Electrons in an oscilloscope are accelerated from rest by a constant force of 8.0*10^16 N over a distance of 15mm. Find (a) the acceleration and (b) the final velocity. Relevant equations: 2...
  18. M

    How does mg = ma follow from F=ma?

    Can somebody explain in simpler terms F=ma and why that can be writtent as mg=ma. Which finally can be written as g=a.
  19. U

    Exploring F=ma and its implications in Newton's Second Law

    We have F=ma (Newton 2nd law), and my questions are: 1 Between F and a, which is the cause of the other? or is it a circular argument? 2 If it is accepted as a kind of circular argument, then a=F/m, then under suitable unit transformation and for a given m, then F is a kind of...
  20. G

    Freshman Electric Engineer Explores Meaning of F=ma

    I'm a freshman who majors in electric engineering. Before several days, I studied for my exam on mathematics. Accidently, an interesting idea hit me! If my idea is wrong or meaningless, I welcome threads to explain why. ----------------------------------------- The meaning of...
  21. B

    What Physics Formula Applies to Particles Smaller Than 10^-10?

    Force=mass X acceleration is used for objects larger than 10^-10 but what formula is used for particles smaller than 10^-10? Also when squaring light in E=MC^2 what would light be? - 9 X 10^35?
  22. H

    How Does Newton's Second Law Adapt to Relativistic Speeds?

    In Newtonian Physics, a force on a object is equal to its mass times acceleration. This is Newton's Second Law. But in relativity, when the acceleration approaches the speed of light, Newton's Second Law starts to become less accurate because to accelerate a mass more you must keep adding more...
  23. E

    Newbie Needs Help: If F=ma, what gives?

    Hi, I'm new here. I hope this is the right area for this question. I've been reading wikipedia all day trying to figure this one out, and can't so any help will be much appreciated. Question: If F=ma, than m=F/a, right? So logically if an object has no force being applied to it that...
  24. D

    Solve f=ma Problem: Find Acceleration, Forces on Blocks

    Homework Statement three blocks (m1=2kg, m2=3kg, m3= 4kg) are in contact with each other on a frictionless, horizontal surface as shown below. a horizontal force f=18n is applied to m1. blocks look like this --force-->(m1)(m2)(m3) find the acceleration of the blocks find the magnitudes...
  25. E

    Unraveling the Mystery of F=ma: Understanding Mass

    Homework Statement Why F=ma? And what is mass? Homework Equations The Attempt at a Solution
  26. R

    F=ma in Racing Cars: Exploring the Relationship Between Engine Power and Weight

    explain the following in f=ma a)a racing car has a powerful engine and is made of storng but light weight material b)a car with a small engine can still accelerate rapidly please help me i need model answers thanks soooooo much:biggrin: :cry: :biggrin:
  27. F

    Why Does Friction Force Matter When Applying F=ma to a Vehicle?

    If f = ma, then in a case of a vehicle accelerating/decelerating why does there need to be a friction force? Say you had no friction force (I know this is not possible) and a car sitting on level ground, then apply a force from a high powered fan (Drag) to the front of the car. why does this...
  28. M

    F=ma for extended objects and movement of CM

    OK, so for a small particle, \Sigma F=ma is very straight forward. If two forces are applied to that particle, the particle accelerates, which is determined by the summation of the forces applied. But what if the object is extended one, say, a solid uniform rod (1 kg). Also, imagine that...
  29. H

    F=ma, what is m actually means?

    My maths teacher taught me that vector cannot divide vector but the physics states that F and A are vectors so m=F/A, what m means?:confused: are there any differences about maths vector and phy vectors?:smile:
  30. N

    F=ma: definition? law? neither?

    Hi all, sorry if this has been done to death in schools everywhere for three centuries, but I haven't seen any textbook that really answers it for me. I understand Newtonian mechanics, at least at the level of solving exam questions. But ever since I decided to go back and relearn everything...
  31. L

    Question Concerning F=ma and FBDs.

    Ok, I know that, using a FBD, one is susposed to use \sum F = m a My question is what order do you put the forces that \sum F equal An example might help me explain my question. Lets take a block of wood that is supported by a string. The only forces acting on it are mg and T So...
  32. B

    When should the negative sign be included in acceleration for F=ma?

    Would someone explain to me when to include the negative into the acceleration a, for F=ma. I know if it is a vector you don't include the sign. But sometimes it seems almost arbitrary in textbooks when they include the negative sign and when they don't. I hope you know what I mean. I know if it...
  33. C

    F=ma proof and understanding force

    general force is a push or pull. how this push or pull is equal to mass x acceleration. one more doubt. a ball is released from rest from the top of a building. initial velocity=0.after 1sec velocity is 9.81m/sec. so acceleration is 9.81m/sqs. so force that caused the ball to fall...
  34. K

    Help pleeeese (validity of f=ma, mass of diff.temp objects)

    help pleeeese~~ (validity of f=ma, mass of diff.temp objects) :cry: please help me~ desperate... 1. is f=ma valid in all situations? explain your reasons~ 2. is the mass of a hot frying pan different from a cold frying pan? why? thank you~~~
  35. J

    First Formulation of Second Law as F=ma ?

    First Formulation of Second Law as "F=ma"? Newton expressed his Second Law of Motion as .Who was the first to put it into the modern form F=ma? Was it Descartes?
  36. G

    Why is the slope of the Fa graph not equal to m in this Atwood machine setup?

    We've been given a lab in physics class to verify that F=ma graphically. To do this we had a cart with weights on top be pulled by a string with weights on the other end over a pully pull the cart down, bringing weights off the cart to the end of the string to keep the mass constant, but...
  37. S

    How can I design a lab to demonstrate F=ma using masses and pulleys?

    I have to design a lab to support that F=ma. we are using masses and pulleys but I'm not sure how to set this experiment up. anyone got any ideas? :confused: thanks in advance 4 any help u can give me sarah
  38. F

    Designing Lab to Prove F=ma with Spring Scale, Mass & String

    I am designing a lab to prove that F=ma. However i am only using a spring scale, 1 kg mass, string. I have come up with a procedure where you would attach the mass to the scale and accelerate the unit upward, recording the time it takes the unit to accelerate from 0-1m and the force shown in the...
  39. M

    Calculating Kinetic Friction Using F=ma and X_0*K

    a block of mass M is held on a horizontal table against a compressed horizontal (massless) spring. When released from rest, the block is launched along the tabletop and eventually comes to a stop after sliding a total distance L. The initial spring compression is x_0 and the spring constant is...
  40. S

    What Does F=ma Really Mean? A Closer Look at Newton's Law

    I've asked a couple of professors, how can you say F=ma is empirically true unless you define what F and m are. Each basically said they didn't have a perfectly good answer to that question. The most obvious answers (in my opinion) lead to circular definitions. Well, I was thinking about this...
  41. O

    Need help with designing an experiment to prove that F=ma

    Anyone know a simple and non-complicated experiment that I can do to prove this law? Thanks in advance
  42. Rockazella

    Classical Physics & Electron Mass: F=ma?

    I know that QM must be used to describe atomic sized systems, but is classical still applicable? Take an electron for example. I don't the the mass of an electron so I'll just say its m=x. If an electron were to have a force of 10N applied to it, would its acceleration be 10/x, or do these...
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