# Circular Motion

Gold Member
Hi. When a plane travels in a vertical circular loop, what is the provider of the centripetal force, required to produce the circular motion?

At the top of the loop, there is gravity acting towards the center of the circle, so id assume that this is part of it, but what about at the bottom and sides of the circle? Gravity no longer acts towards the center of the circle, since it is always directed downwards. This is where my confusion arises.

Thanks for the help,
Dan.

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What other forces are acting on the plane? Hint: there are a total of 4, couple of which have a bearing besides gravity.

Gold Member
Well there would also be air resistance, but in this case, im neglecting air resistance for the simplicity of the situation. Im just focusing on the force contributing to the centripetal force.

Ok, very good, thats one, but unlikely to help in this circumstance. You could just google a search for forces during flight, or think about why you hear what you do, assuming you have been aboard an aircraft. I'm not trying to make your life miserable, but this forum is dedicated to education. This takes effort on both the part of the teacher and student.

Gold Member
Well aswell as air resistance and gravity, there will be a force provided by the engines, or a thrust as ive heard it called before.

Would the final one be a force opposing the gravity?

Its called lift! Without it you are a bus too big to use the highway.

Gold Member
Ahh ok.

Im still a bit confused though. When travelling in a vertical loop, do both the lift and gravity affect the centripetal force?

Anything that travels in a circle experiences centripetal force. It is the reaction to the forces that keep the path circular. The pilot keeps the plane in it's path using the power of the engines.

Astronuc
Staff Emeritus
Ahh ok.

Im still a bit confused though. When travelling in a vertical loop, do both the lift and gravity affect the centripetal force?
Gravity always works in one direction - down toward the earth's center.

An object traveling in a circle is constantly accelerating because velocity, a vector is constantly changing direction, even if speed (a scalar and magnitude of instanteous velocity) is constant.

Flying horizontally, the lift balances the weight (force of gravity). The forward motion is provided by the thrust of the engine/propeller, and some of the thrust opposes the drag (wind resistance).

As an aircraft turns vertically, more of the lift is provided by the engine/propeller. Most aircraft slow as they begin to turn, unless the pilot increases the engine power (cruising speed is usually at less than full throttle).

The centripetal force is simply mv2/r, where v is the tangential speed and r is the radius of curvature. Gravity affects the net force on a body in a plane. At the bottom of a circular arc one experiences the combined effect of centripetal force and gravity, whereas at the top of an arc, one experiences centripetal force minus gravity. If the centripetal force = gravity, then one can experience temporary weightlessness.