Professor Mac Explains Newton’s First Law of Motion

Professor Mac Explains Newton’s First Law of Motion

Articles, Blog , , , , , , , , , , , , 100 Comments

Oh, Hello. Welcome to my laboratory. My name is Professor Mac, and today I am going
to be talking about Newton’s first law of motion. This is one of three laws which Sir Isaac
Newton published in 1687. The laws explain the interaction of forces
and objects and the way in which the motion of an object is affected by force. So what about the first law. Well the best
way to understand this is for us to do an experiment. Ok, well here is our experimental set-up. We have block of wood here representing our
object. And as you can see it is resting on a very
smooth surface, which is so smooth we can assume that it provides no resistance to the block
moving on it. So what about Newton’s first law. Well it states that an object, such as our
block here, will remain in its current state of rest, in other word not moving, unless
acted upon by an unbalanced force. So lets look at our block. You can see it’s
not moving and it continues to stay that way, so Newton’s first law would suggest that the
forces on the block must be in balance. Otherwise it would start moving. So lets have a look at the forces on the block.
We represent the forces by arrows which show the direction of the force and also the size
of the force. The longer the arrow the larger the force. The first force on the object we consider
is from gravity and it acts vertically down. Looking around the object we can see it is
in contact with the surface of the table. Since we have used Newton’s first law to conclude
that the forces must be in balance, it follows that the force from the table on to the block
must be upwards and equal in size to the gravity force. This means the forces in the vertical
direction are in balance and the block continues to remain stationary in the vertical direction. In the horizontal direction there are no forces
and so the block continues to remain stationary in the horizontal direction. So what if we introduce a horizontal force.
What do you think will happen? Well we can do that by using this piston I
have set up next to the block. When I push the button for the piston to move it will
push the block. Let’s see what happens. (piston whoosh) Well we can see that the block changed from
being stationary to moving horizontally and Newton’s First law tells us that this is because
there was an unbalanced force on the block. Lets run a replay and look at the forces on
the block. We can stop the action just as the piston
contacts the block. Now you can see we have the vertical forces
as before, and also a horizontal force from the piston. The vertical forces are still
in balance so there is no change in the vertical motion of the block. However the unbalanced
piston force pushes the block horizontally, changing the state of the block from being
at rest to it moving horizontally. Just as we would predict using Newton’s First Law. As the block continues to move horizontally
you can see that the vertical forces are still the same and in balance. But what about the
horizontal forces. Well there is no piston force and the highly
polished surface provides no resistance to the motion of the block and therefore there
are no horizontal forces acting on the block. So all forces are in balance resulting in
no change in the motion of the block. It is still moving but it doesn’t change with
time. It is constant motion. This observation, which may at first seem
surprising, is consistent with the second part of Newton’s first law, which states
that an object will continue in its state of uniform motion, in a straight line, unless
acted upon by an unbalanced force. So there we have Newton’s First Law of Motion.
In summary we observed, during our experiment, that an object will continue in its state
of rest unless acted upon by an unbalanced force. And we also observed that it will continue
in its state of uniform motion, in a straight line, when all forces are in balance. So here is a question for you. What if the
block moved on a surface which resisted the motion of the block. What do you think would
happen? Can you draw a diagram of the forces on the block? Well for some help in working out the answer,
and to see what else I’m doing, why don’t you come and visit me at my website Well, thank you for very much for joining
me today, and I look forward to you visiting again. From me, Professor Mac, until next time, “All
the best”. Bye

100 thoughts on “Professor Mac Explains Newton’s First Law of Motion

  • learnwithmac Post author

    Hi Thermospecialist, I agree that it is important to define force. However I have assumed that the viewer has had some introduction to forces before viewing the video. I need to make some assumptions otherwise the video would be too long. I may make a video on defining force, mass and acceleration to complement this video at a future date. Thanks for your feedback. Mac

  • rishabh kothari Post author

    awesome video sir mac 🙂

  • learnwithmac Post author

    Thanks Rishabh.


  • Rajendra Nadagouda Post author

    Thanks it helped in understanding the first law of motion

  • learnwithmac Post author

    Pleased that you found it helpful Rajendra.


  • Thermospecialist Post author

    Unbalanced forces do not exist, but in theoretical frames of reference only. With an as yet not existing correct understanding of forces, Newton's third law applies regardless what reference system is considered. This correct understanding also explains inertia. See: watch?v=91bCIC5krik

  • Skyardian Post author

    hello sir,
    what i want to ask is that
    if the force of the piston is 2000 N to the block
    then when will the block would stop?

  • learnwithmac Post author

    Hi Syardian. The answer may surprise you. If there is no friction on the table and no air resistance then the block will never stop. It will move forever at the same velocity as it had when it left the piston since there is zero net force acting on it. This is what the first law tells us. If there is zero net force on the block then it will stay at rest or keeping moving. If there is friction it will stop and you would need to use Newton's second law to calculate the stop distance. Mac

  • Vikas Sachdeva Post author

    awsome video

  • learnwithmac Post author

    Thanks Vikas


  • Tabi Kitten Post author


  • learnwithmac Post author

    Thanks Max


  • learnwithmac Post author

    Hi Alex, I don't understand your question. Would you clarify please?


  • learnwithmac Post author

    I'm glad it helped Suhas.


  • ABDUL WAHID Post author

    hey mac! u deserve more than merely being liked by us on youtube…. i love ur explanations a lot

  • learnwithmac Post author

    Thanks for your feedback Abdul.


  • Ensign Gaming Post author

    Hey Professor Mac.

    I have a question. Please answer it.

    So the wooden box exert a force from the piston and it is continue to move forward right? So why it doesnt change the postion. It cannot move to a straight line I think it should move and will fall from the ground because. I think it cannot move a straight line tho?


  • learnwithmac Post author

    Hi Jason, thanks for your question. Why do you feel the box (block) will not move in a straight line to the right? If the block was moving and you wanted it to change direction you would need to push it to change direction. Once the block leaves contact with the piston in the video there are no other forces acting on it (assuming zero friction and zero air resistance). The block will therefore continue in a straight line until a force acts on it to change its direction. Mac

  • SCIENCE ZONE Post author

    1)what is Fnormal mac?
    2)according to newton ,body continues its motion untill no external force is applied on it but why will the block or object in motion stops after some time even if we dont touch it ?

  • learnwithmac Post author

    Hi Sunny, Fnormal is the force on the block by the table. It is called Fnormal to indicate the direction of the force is normal (meaning it is at an angle of ninety degrees to the surface). In the real world there are friction forces as well as air resistance. So if we were to try to do this experiment in the real world we would find that the block would slow down due to the friction and air resistance forces. Regards Mac

  • SCIENCE ZONE Post author

    thanx mac

  • Angel Dark Post author

    Please answer my assignment as soon as possible.It needs to be passed by tomorrow please help me and please explain why that is the answer.Here is my assignment:A 100N weight rest on a 30 degrees inclined plane.Neglecting friction,how much pull must one exert to bring the weight up the plane?

  • Dijonalis Harris Post author

    God bless you professor, with your ilustration I can undarstand these things…. thank you verry much

  • learnwithmac Post author

    Thanks for your feedback Dijonalis. Good luck in your studies.

    Regards Mac

  • BlurryDruid Post author

    Good Video, I used it For my Physics class. It helped all 3 of them. What animating software did you use? It looks pretty cool and I want to create something similar too 🙂

  • Ivana Egenti Post author

    thanks mac the video was a little creepy but it helped me with my home work

  • Ahmad AE Post author

    the best of the best

  • Manisha Pandey Post author

    hi mac, 
    so balance force is keeping an object rest and the object will continue to move untill another force is applied?

  • Paio Councillor Post author

    So on a surface with friction the vertical motion will slow the object down

  • Nakawele Sakala Post author

    I am writing a physics cycle test tomorrow about three of Newtons laws so am going through all of them to help me understand them more and so far this video helps so much, it explains the law very clearly and practically…

  • Freya Nair Post author

    great video 

  • Jaber Kabiri Post author

    This was extremely helpful

  • aidan byrne Post author

    Great vidio! Im using it to revise for my year eight assesment, but wouldn't air resistance affect the speed and acceleration unless the experiment in space? I'm confused because you didn't say whether it was done in a vacume or not.

  • Diego Olivarez Post author

    For this experiment, wouldn't the wood block be affected by wind resistance, causing it to slow down eventually?  Thanks!

  • Nathan Zou Post author

    Wouldn't the block go on forever because the table causes no resistance? Thanks Professor Mac!

  • gul [email protected] Post author

    tahnx prof mac….. using this to help my son with his phsics and also learning myself
    do you have videos on chemistry??

  • Emelia Oppong Post author

    hi professor mac thank you 

  • Elias Post author

    this will help me on my test tomorrow thank you very much. 
    and by the way i like your accent 😀

  • Isabel Janeth Lòpez M. Post author

    Thank you so much for sharing, I will use it for my class.

  • nalluri likhith Post author

    i have a doubt, the velocity of the block doesn't change when we neglect air resistance and friction of surface. But in the universe there is no resistance acting on the body so when we apply some force on a body in universe the body moves with a velocity will it be constant? thanks

  • Era Madaria Post author

    ty u sooo much sir

  • Codo Sacho Post author

    is the human considered as an object ?? and what is Fnormal??
    thanks in advance

  • Cod4uandme Post author

    Hey thanks for newtons first law this really helped me!

  • Cod4uandme Post author

    I was wondering something… what is ''ideal frictionless?'' Can someone tell me this? thanks this will help

  • learnwithmac Post author

    Hi Nico, I can't reply to your comment as you have that option disabled. Friction exists in the world around us. It is not possible to have frictionless (zero friction) surfaces. However we sometimes consider what would happen if a surface was frictionless to consider the application of a theory in the extreme case. This can give direction on how we would ideally like to design objects. For example, in an engine we know that if we reduce friction to a minimum the engine is more efficient as there is less resistance to the engine as it operates. Regards Mac

  • Nekaigo Post author

    Your three videos are the perfect well-rounded videos to watch when you don't understand the laws of motion. They briefly, but they explain in a very well way how these laws work. Thanks! 😀

  • Ahmed Fadl Post author

    I didnt understand the first expirement

  • mirror talk Post author

    Well presented!! Newton first law should be understood by all ….If the forces are in balance so are we.

  • mirror talk Post author

    Great to see that Sir Isaac Newton is getting the big hits on YouTube and once again his renewed placement in history. He is a classic giant!!

  • mirror talk Post author

    Yes right on!
    I saw the Newton show at the New York public library years ago. At the show they had his mathematical work and manuscripts on Principia and the Calculus.
    It was so beautifu, elegant and poetic!
    Reminded me so much of the drawings and writings of Leonardo Da Vinci…
    I love to study it has been my hobby since a kid .I always think of the greats even if I am riding my bicycle! Newton laws of motion top on my list, still is.

  • aurora00145 Post author

    But… Isn't there air resistance acting on the block which causes it to slow down as it is sliding? I haven't been able to grasp the concept completely. So, for example, how would you answer the following question: when you sit on a cushion, what is the effect of your weight on the cushion? 

  • Anil Kanwat Post author

    hi mac? would you mind explaining me the difference between external force and external agency?
    because i remember force is an external agency which tries or tries to change the state of body.


    Big thanks for educating the virtual audience

  • Melker Post author

    i r8 8/8 m8

  • Irish Patel Post author

     the air resistance slows down the object?

  • abigail diaz Post author

    thanks this is perfect cause i have a huge science test tomorrow and i want to ace it. 

  • KR DG Post author

    Hello Sir, I have a question! What would happen with my tea if I stop abruptly?

    If I'm walking in the horizontal direction holding a cup of tea I believed that whiles  I'm walking, I am doing it in one direction –in straight line – however, if I stop abruptly, I would apply a resultant force; this force will cause my tea within my cup to change its state of motion.   
          My applied resultant force will cause my tea to move forward – further away from its position within my cup- and faster. The direction in which my tea would move, would be forward and out of my cup
    I'm I right?

  • Sasha Wagner Post author

    So in summary… Objects at rest may Remain at rest unless an unbalanced force acts upon it.

  • Robert Smith Post author

    This guy freaks me out

  • Rowan Blanchard Post author

    i do like it

  • Julius Calderon Post author

    Why are the three Newton's law did not have a tittle or name?

  • Daniel Cesarini Post author

    Mac, you are a legend. You have helped me so much with my Science test. When I get an A+, I will be sure to thank you in my acceptance speech.

  • medicore0000 Post author

    What if the table extended onward out of the atmosphere of the Earth and into space. Let's assume that it feels no resistance at all (not from the air nor the surface). Would the block continue to move and completely escape the Earth's gravity?

    The only change I can think of is the angle at which gravity starts pulling on the object. As the earth curves away gravity should start pulling on it more and more from the back side eventually slowing it down to a stop, reversing its direction of motion and pulling it back to the piston. It should then hit the piston with exactly the same amount of force that the piston hit it the box the first place.

    I think I just answered my own question while writing this. Anyway if you see anything wrong here let me know.

  • Sk Sadi Post author

    Hello learnwithmac please explain with animation Black hole low Rs=2GM/c2.

  • Aatreyee Bhattacharya Post author

    Hello! I just wanted to ask that, what if two unbalanced horizontal force that is two pistons from opposite sides acted upon the box? And moreover why do you keep calling it an unbalanced force? What if the force acting horizontally was balanced? What would happen then?

  • Marrius Eratic Post author

    if I made a tower out of boxes and I build it too the point at which it can no longer hold it's own weight, would it fall straight down? And if so would it stop at the point where it's no longer too heavy for it's own weight? Which would be after the bottom block was destroyed and if it's equally pushing up wouldn't that mean two boxes would be destroyed? Hope this makes sense t.i.a. 8[

  • learnwithmac Post author

    +Marrius Eratic Hi Marrius. Thanks for your question. Newton's first law does not address failure, it only tells us the response of an object to force in terms of its motion. In the example you have described, the force due the weight of the boxes in the tower eventually exceeds the force carrying capability of the bottom box. The box then fails to be able to continue to carry the force and collapses (often referred to as a buckling failure). The tower would try and collapse straight down as you put it, but in practice the boxes would interact with each other introducing random interaction forces which would result in the tower collapsing in a random direction. The force on the bottom box is higher than any of the other boxes and it would collapse first assuming all boxes had the same strength. Note that to understand this you need to realise that the force experienced by the box material increases linearly from the top of the box tower to the very bottom of the tower. So the highest force experienced is in the bottom box at the edge close to the ground. Regards Mac

  • Mary Lu Post author

    do you have an email that we can ask questions on, or maybe a tutoring site?

  • Gēoffrey Eng Ātkinson Post author

    sorry professor Marc.. that object didn't stop because their was no friction on it??? if yes can you give me an example of any surface like that please…

  • Kavita Dubey Post author

    Thanks mac

  • HerobrineCraft Post author

    Professor Mac lives in a black hole, there is no air/air resistance and when there is nothing, it's a black hole 😀

  • Harjinder Sandhu Post author

    You legend, best teacher ever

  • music master Post author

    this is so freaking creepy

  • vikash sharma Post author


  • Luka Staveley Post author

    You have no eyelashes ????????

  • Navarin James Post author

    what's the name of the soundtrack

  • Richard Richie Post author

    All of your videos are great, easy to understand…thanks professor Mac! please add more videos.

  • Anupa Unni Post author

    i love you mac

  • RAJU KUMAR Post author

    Thank you proffesor your videos i understand very well

  • musdafe maxamed Post author

    but tou are not talking maths why proff special indices

  • Abbas Balti Post author

    your videos are nice and easy to undersatand for any person….you are doing well job…

  • Hydra Post author

    Our teacher made us watch this

  • Momo eater Post author

    so if there were no external forces and I pushed something would it keep on moving forever. If yes then does it not need any energy to keep it moving.

  • Fripouillex Post author

    Guardians of the galaxy is better 😀

  • Papa Groovy Post author

    he just stares into youre soul

  • Ashton Hyden Post author


  • Ashton Hyden Post author

    this is so creepy

  • Yogesh Yogi Post author

    please upload more vedio. I learn a lot and very clearly from this . please please please upload more vedios

  • eliot Post author

    dad, is that you?

  • amjad aziz Post author


  • Peter Tosh Post author

    aa aaa aaaa

  • 201 Stuff Post author

    i'm gonna play fortnite tonight

  • Mathias Bergøy Post author


  • SAMMYBOI _128 Post author

    Hello, this is Sam Ogden, I am hoping that one day Mrs. Jordan’s future class will see this and they will know that I was here

  • SAMMYBOI _128 Post author

    Hello, this is Sam Ogden, I am hoping that one day Mrs. Jordan’s future class will see this and they will know that I was here

  • John Shepphard Post author

    this video is so nasty i think i need to bleach my eyeballs

  • Maxwell Keding Post author

    I'm really concerned with the population that thinks that this is a good video…

    Because Its Not

  • Spenf Boulagwai Post author


  • Javyer Burtner Post author

    Wouldn’t the block slow down though? Wind/air resistance would slow it to a stop, no matter how smooth the surface is.

  • Franky Uk Post author

    I would suggest that before you use the theory of gravity as a force, you first scientifically prove what it is, how it works and that it exists…

Leave a Reply

Your email address will not be published. Required fields are marked *