People and earth pull on each other, so why do people fall?

  • Thread starter Thread starter Taharok
  • Start date Start date
  • Tags Tags
    Earth Fall Pull
AI Thread Summary
Daniel's weight of 800 Newtons results in an equal and opposite force exerted on Earth, as per Newton's Third Law. Despite this mutual attraction, Daniel can trip and fall due to the significant difference in mass between him and the Earth, which leads to a much greater acceleration for Daniel when he falls. The acceleration of the Earth towards Daniel is negligible, making it imperceptible. The discussion highlights that while both bodies exert forces on each other, the effects are vastly different due to their mass disparity. This understanding clarifies why people can fall despite the gravitational pull between them and the Earth.
Taharok
Messages
1
Reaction score
0

Homework Statement



Daniel's weight is 800 Newtons. According to Newton's Third Law, if the Earth pulls on Daniel with a force of 800 Newtons, then Daniel pulls on Earth with a force of 800 Newtons in the opposite direction. Why then is Daniel able to trip and fall down to the ground?

Homework Equations



None

The Attempt at a Solution



Well, I've been stuck on this for a while now. I remember learning something about this with a leaf falling, but I can't remember/find it anymore.

I do have one theory, however. Even though I said there are no relevant equations, I believe I can use Newton's Second Law (F = ma) to figure out this problem. I need to rearrange this equation to solve for acceleration, as so: a = F / m. If force F is the same for both the Earth and for Daniel, then the only changing variable is m. The Earth has an extremely higher mass than Daniel, so the acceleration for the small force of 800 Newtons is so small, it's nearly nonexistent. However, Daniel's mass is much smaller, so the force of 800 Newtons causes his acceleration to be considerably higher than the earth's, so much as to make him fall down.
 
Physics news on Phys.org
I think you've got the right idea.

But I wonder about the wording of the question. Intuitively, why would Daniel not fall down? i.e. Why would the mutual attraction of Earth and boy adversely affect his movement toward the Earth upon tripping?
 
Your reasoning is right. If Daniel trips, he falls towards the Earth with a noticeable acceleration. Although the Earth DOES move up towards Daniel, its acceleration when it does that is so tiny that you can't tell it's happening.
 
Luckily, or I would be bouncing up and down and the solar system would probably get disrupted every time someone in Australia (hey guys!) jumps up and down or someone takes an elevator from the basement to the 20th floor.

PS Taharok, it might be "fun" for you to actually calculate the acceleration of the Earth due to Daniel falling, and its (relative) change in velocity if this fall took, say, half a second. :)
 
Kindly see the attached pdf. My attempt to solve it, is in it. I'm wondering if my solution is right. My idea is this: At any point of time, the ball may be assumed to be at an incline which is at an angle of θ(kindly see both the pics in the pdf file). The value of θ will continuously change and so will the value of friction. I'm not able to figure out, why my solution is wrong, if it is wrong .
TL;DR Summary: I came across this question from a Sri Lankan A-level textbook. Question - An ice cube with a length of 10 cm is immersed in water at 0 °C. An observer observes the ice cube from the water, and it seems to be 7.75 cm long. If the refractive index of water is 4/3, find the height of the ice cube immersed in the water. I could not understand how the apparent height of the ice cube in the water depends on the height of the ice cube immersed in the water. Does anyone have an...
Back
Top