The question I am looking at is: "When an object falls freely under the influence of gravity there is a net force mg exerted on it by the earth. Yet by newton's third law the object exerts an equal opposite force on the earth. Why doesn't the earth move?"(adsbygoogle = window.adsbygoogle || []).push({});

My actual problem isn't with the question, but with the solution, which I read after I solved it. To solve the problem, the gave a simple calculation to find the answer. The imagined a 1 kg object, and they approximated earth's mass to be of the order of 10^25 kg.

They stated that [itex]F_{_{Earth}} = F_{_{Object}}\rightarrow(10^{25} kg)a = 1 kg\cdot9.8m/s^2[/itex] And solving for a would give [itex]9.8\cdot10^{-25} m/s^2[/itex]

So, the gravitational acceleration the object provides would be that minute number. But say the object had a mass of 100 kg. Re-doing the calculations would yield [itex]9.8\cdot10^{-23}m/s^2[/itex] Why does this gravitational acceleration change? Shouldn't Earth's gravitational acceleration change then? I now my thinking is erroneous somehow, but I can't seem to figure out why. Does it maybe have to do with Earth's mass be constant? I'm not entirely sure.

**Physics Forums | Science Articles, Homework Help, Discussion**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: Accelerations Due To Gravity

**Physics Forums | Science Articles, Homework Help, Discussion**