Question about Third Newton Law

In summary, when jumping, you use your mass and a bit more to create greater acceleration away from Earth.
  • #1
AlbertE97
10
0
If I jump, I accelerate away from Earth.
However, if I drop a human on the ground, he doesn't accelerate away from the Earth.

In both cases the force used on the Earth is about the same, but acceleration away from the Earth exists in one case and doesn't exist in another case. Why so?

(not a homework question but one I thought of myself)(English is my 2nd language)
 
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  • #2
AlbertE97 said:
If I jump, I accelerate away from Earth.
Only while still in contact with the ground, using your muscles.
AlbertE97 said:
In both cases the force used on the Earth is about the same
It is not.
 
  • #3
"It is not."
I understand that they're different. But they're not that much different - both are not negligible and not huge. When you jump, you use your mass + a bit more. When you fall, you use your mass + a bit more.
 
  • #4
AlbertE97 said:
"It is not."
I understand that they're different. But they're not that much different - both are not negligible and not huge. When you jump, you use your mass + a bit more. When you fall, you use your mass + a bit more.
No, when you jump your feet push Earth quite hard (with more than your gravitational force), when you fall your feet do not push Earth at all.

Please do not remove your posts, others might have the same question and be happy to find an old thread about it (also via google).
 
  • #5
You're right that acceleration exists away from the Earth in both cases. But, when you fall, you start out with a negative velocity, so that when you are finished accelerating away from the earth, you end up with a zero velocity. When you jump, you start out with zero velocity, you accelerate away from the earth, and you end up with positive velocity.
 
  • #6
Thanks, Lsos. I think that you have decoded the OP correctly. The distinction is not between jumping and falling. It is between jumping and landing.
 
  • #7
Lsos said:
You're right that acceleration exists away from the Earth in both cases. But, when you fall, you start out with a negative velocity, so that when you are finished accelerating away from the earth, you end up with a zero velocity. When you jump, you start out with zero velocity, you accelerate away from the earth, and you end up with positive velocity.

Errr... you can start with 0 velocity, nothing seems to prevent it. That is 0 velocity downward towards Earth's core. 0 velocity is not the same as negative velocity. 0 is non-negative. Sorry to nitpick... I apologize for rudeness.:s

Imagine if you are Felix Baumgartner and balloon stays at constant altitude.Then you jump out of the balloon, or walk out of the balloon rather. Ground vanishes beneath your feet, when you take step outside the cabin of the balloon. Then begins the air drag and gravity effects. Essentially the lift force from balloon, stops at this point indeed.With regards to jumping upwards, from the ground...

Certainly your own mass stays the same during jumping and standing still, on earth.

But when you jump upwards, you basically squat down first (bend your knees)... Then your muscles engage and you are able to jump upwards. Does your weight, change?

Is it simply so that the weight doesn't change? Does there become increased net force towards earth, when you push hard from your bent knees? (increased net force when compared to simply standing still on your legs).

Increased net force toward earth, would mean that there exist equally great counter-force away from the earth? Certainly it feels like your body has more momentum outward from earth, when you jump with the squatting technique... :eek:

Weight happens because of gravity, right? Gravity is fundamental force in universe.

But gravity strength, depends on mass? My mass stays the same, Earth mass stays the same, when I jump upwards from earth. ?:)
 
  • #8
AlbertE97 said:
If I jump, I accelerate away from Earth.

Technically speaking, the following happens because of Newton's third law.

You accelerate away from earth, AND EARTH accelerate away from YOU.Earth acceleration is really small, though. Because Earth has massive inertia, it is difficult to move Earth from orbit, by humans jumping off from earth.
 
  • #9
I understood this question right after putting it on this forum and I erased everything in the post (before anyone posted anything) because there is no 'delete post' button on this forum, but for some reason mods decided to recover the post... just ignore this post...
 
  • #10
I'm not sure I follow this question clearly. This seems a very simple matter - a human being is not a rigid object. When a person lands after falling, he/she will absorb the impact with their body, so the force is actually spread through the body. But there is still an upward force. The Earth will tend to move away from you, and you will tend to move away from the earth. It's just not apparent from how your flexible body reacts. If you replace the human body with a rigid object, say a steel ball of same mass and drop onto a hard surface, the object doesn't just stop. There will most definitely be an acceleration away from the earth. Several times until the force is dissipated. Have I misunderstood the question and the forces involved?
 
  • #11
Graeme M said:
I'm not sure I follow this question clearly. This seems a very simple matter - a human being is not a rigid object. When a person lands after falling, he/she will absorb the impact with their body, so the force is actually spread through the body. But there is still an upward force. The Earth will tend to move away from you, and you will tend to move away from the earth. It's just not apparent from how your flexible body reacts. If you replace the human body with a rigid object, say a steel ball of same mass and drop onto a hard surface, the object doesn't just stop. There will most definitely be an acceleration away from the earth. Several times until the force is dissipated. Have I misunderstood the question and the forces involved?
Like I said, ignore this post..
 
  • #12
I think this thread is done.
 

FAQ: Question about Third Newton Law

What is Newton's Third Law of Motion?

Newton's Third Law of Motion states that for every action, there is an equal and opposite reaction. This means that when one object exerts a force on another object, the second object exerts an equal force in the opposite direction on the first object.

How does Newton's Third Law apply to everyday life?

This law can be seen in everyday life, such as when you push on a door to open it. Your force is applied to the door, and the door exerts an equal and opposite force on you, allowing the door to open.

What are some examples of Newton's Third Law in action?

Some examples include a rocket launching into space, a person jumping on a trampoline, and a ball bouncing off a wall. In all of these scenarios, there is an equal and opposite force at play.

How does Newton's Third Law relate to the other laws of motion?

Newton's Third Law is part of Newton's three laws of motion, which work together to explain how objects move. The first law states that an object at rest will stay at rest, and an object in motion will stay in motion, unless acted upon by an external force. The second law relates force, mass, and acceleration. And the third law explains the equal and opposite forces at play.

Are there any exceptions to Newton's Third Law?

There are a few exceptions to this law, such as when objects are not in direct contact with each other or when there is an unbalanced force acting on one of the objects. In these cases, the equal and opposite forces may not be noticeable, but they are still present.

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