Can gravity have a different pull at a different location?

Question

When I ride my bike, some hills look hard but are easy and some look easy but are hard. Is this an optical illusion or can gravity have a different pull at different places?

Answer 1

Most simply, yes gravity will vary where one is. However, on earth gravity is essentially static at 9.8m/s. But gravity does not exist only on earth, rather every object. It will depend on mass and spin, so the gravity a person produces is EXTREMELY small, while a planet or sun produces a notieable amount.

Two objects will interact according the universal gravitational equation, F = GMm/r^2, where the important part is that as distance increases the effect of gravity decreases very quickly (r^2).

If you were to put the distance between you and the center of the earth in while you were on two different hills, there may be a total difference of 10m (33 feet). However, this is infentesimally small compared to the actual radius of the earth.

The net result...the actual change in gravity is MUCH too small for us to detect, but there really is a change.

There other possible result is like you said that there is an optical illusion, and the grade of the hills isn't what they seem to be. that happens all the time when I ride my bike. Hope this helps.

Answer 2

Yes, it does. The NASA GRACE mission has provided some fascinating maps of the strength of gravity on the surface of the earth at various times. See the references. But these variations are much smaller than you could ever detect on a bicycle.

How hard or easy a hill is for you depends on the slope, length, and variation compared to you and your bicycle. How an upcoming hill looks to you is an entirely different matter of perception. If you are standing still in hilly terrain with no other visual clues, you can't even tell whether the road ahead of you is uphill or downhill. The difference between a comfortable ride and a struggle can be just a degree or two, and that's hard to judge by eye.

Answer 3

Technically, yes, but the effects are negligible. In terms of you riding your bike, there really isn't any difference.

Gravitational pull is determined by the size of the two bodies and the distance between their centers of gravity. This means that your weight at sea level will actually be greater (though only to a small degree) than your weight at the top of Mt. Everest.

Since the hills that you're taking are of far lesser heights, there really is no difference.

Answer 4

We have a hill we call "Gravity Hill" that seems harder than it should be and we suspect a gravity spike on the slope.
Really, gravity is a function of the radius from the center of mass of the Earth, but the difference in elevation of a hill is negligible compared to the radius of the Earth.

More likely it could have to do with topography. You might want to get a Polar S725 or similar cyclocomputer that measures altitude changes. You will find that it is very sensitive to temperature and changes in humidity. It will give you a feel for the grade of hills and your ability to ascend a given grade and duration.

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Answer 5

It does have a different pull in different locations, although it shouldn't be a noticable amount

the force of gravity= G(mass of body)(mass of planet)/(distance^2)

F=GMm/r^2

it depends on how far you are from the the center of the earth, but also on the density of the material underneath you
if you were standing on a large rock, you would feel more of a pull than if you were floating in the middle of the pacific ocean

this would not affect your bike riding
changes in gravity do not have a large enough effect for you to feel it

Answer 6

The example you are talking about would be an illusion (not optical BTW.) If there was a difference it would be negligible and you wouldn't notice it on a bike. The only measurable differences occur with drastic altitude changes. For example, at sea level versus on top of Mount Everest.
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Answer 7

Here's the Yahoo News article about that weird Canadian gravity....

http://news.yahoo.com/s/livescience/20070510/sc_livescience/weirdgravityincanadablamedonheftyglaciers;_ylt=Aql4_Wpjuhkp_QlLhKEO43dxieAA

It's a long link, it may need some sort of cut-and-paste job, sorry. -_-

Point is, it can happen, but the change is too small for it to matter so much on a bicycle. What I would do is check your tires on your bike, make sure there aren't any odd wear patterns. And if that isn't the case, check the hills themselves, some of them may have traction issues (slicker road or grassy surface equals a harder climb), take a very slight curve, lean slightly to one side or another....a lot of things could throw this off.

Hope this helps...thanks for your time! ^_^

Answer 8

It's got to be an illusion. Although the intensity of gravity does vary slightly at different regions on Earth, the difference is far too tiny for us to notice.

Answer 9

I know there is a spot in Canada where the gravity doesn't pull as hard, but I'm not sure how common that is. The story was just on CNN earlier this week: maybe you can still find it.

Answer 10

The pull of gravity [ weight W = mg ] on a body may be different at different locations

The pull depends on 'g' the acceleration due to gravity

Using Newton's law of gravitation,

mg = GMm / r^2

where ' M ' is mass of earth and ' r' is distance between body and center of earth, G is Universal gravitational constant.

g =GM/r^2

Thus with change in distance 'r' ,the value of 'g' will change

Earth's rotation reduces 'g' [maximum reduction at equator and no reduction at poles]

Inside the earth 'g' is directly proportional to distance from the center [ 'g' is zero at the center of earth]

But variation of 'g' at nearby places on the surface of earth is very very small and cannot be noticed

In your case, it is how you perceive the SLOPE ?

The perception is subjective and hence the sensory illusion .

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