# Centripital force on 3d bodies

1. Apr 14, 2010

### firavia

I have created such a thread in the past but it was misinterpreted and I havent been given the help I needed , this time I shall explain more about what is going wrong through a figure .

topic:
when a 3d body is going at constant velocity in a straight line and suddenly a force in its center of gravity was applied and has a certain angle with its initial velocity vecotr the body will make a turn and it will go in a curvilinear path if this force persist , my question why does that body when it turns it turns like in case "1" in the image below and not like in case 2 in the image:

and when does a body rotate like in case 2 ?

if the same body shown in the figure has a propeller engine that when is activated its force acts on its center of gravity and perpendicular to it s initial velocity will the body rotate the same way as in case 1 or it shall go sideways like in case 2 ?

Last edited by a moderator: Apr 25, 2017
2. Apr 14, 2010

### PhanthomJay

if the object moving in a straight line with constant velocity, and not rotating, is acted on by a force which acts at an angle to the initial path, applied thru its center of mass, then it must take a curvilinear path as shown in Option 2, not as shown in Option 1. It cannot rotate if there is no net torque applied to the object.

3. Apr 14, 2010

### rcgldr

A linear force is required to change the objects path, an angular torque is required to change the objects orientation. In the case of a car or plane in a turn, then there is both a force and a torque involved.

4. Apr 15, 2010

### firavia

Why in the case of a 3d object hinged with a cable that is attached at a center like a pendulum the centripital force which is always perpendicular to the object center of gravity do orient the object and make it revolve like in case "1" , what is the difference ?

and in the case of an airplane if the plane bank it must go in a curvilinear path like in case "2" because of the horizental component of its lift force , but thats not what really happen because when a plane do bank it go in a curvilinear path and it change its orientation like in case "1"?
and in artificial satelites built by men when they orbit the earth they do act like a pendulum where in this case the cable of the pendulum is attached to the center of the earth so that the satellite will act like in case 1 in the figure above.!
if it is not the case in a plane what does make a plane change orientation while going in a curvilinear path other thn the horizental component of "lift" force ?

sorry again for my bad english.

5. Apr 15, 2010

### rcgldr

If the object had sufficient angular inertia, and if the attachment point was a low friction bearing then object would resemble case 2 for a while, but any friction at point of attachment would generate a torque that would eventually spin the object into a case 1 condistion.

If the plane doesn't curve horizontally, then the air flow pushes against the side of the airplane and the vertically oriented stabilizer, and weather vane effect causes the plane to yaw into the direction it's headed.

Satellites in orbit are virtually friction free and their rate of rotation is independent of their orbital path. Depending on the satellite, small thrusters may be used to keep it facing some far away object (Hubble telescope) or facing the earth (some communications satellites).

6. Apr 16, 2010

### firavia

I reaaly do thank you , cause U HAVE finnaly convinced me it seems every case has its conditions , thank you jeff : )