centrifugal force
(noun)
the apparent outward force that draws a rotating body away from the center of rotation
Examples of centrifugal force in the following topics:
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The Coriolois Force
- When Newton's laws are transformed to a uniformly rotating frame of reference, the Coriolis and centrifugal forces appear.
- Both forces are proportional to the mass of the object.
- The Coriolis force is proportional to the rotation rate, and the centrifugal force is proportional to its square.
- These additional forces are termed inertial forces, fictitious forces, or pseudo-forces.
- However, the observer (red dot) who is standing in the rotating/non-inertial frame of reference (lower part of the picture) sees the object as following a curved path due to the Coriolis and centrifugal forces present in this frame.
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Kinematics of UCM
- Any force or combination of forces can cause a centripetal or radial acceleration.
- Just a few examples are the tension in the rope on a tether ball, the force of Earth's gravity on the Moon, friction between roller skates and a rink floor, a banked roadway's force on a car, and forces on the tube of a spinning centrifuge.
- Any net force causing uniform circular motion is called a centripetal force.
- According to Newton's second law of motion, net force is mass times acceleration.
- Thus, the magnitude of centripetal force $F_c$ is:
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Force at an Angle to Displacement
- A force does not have to, and rarely does, act on an object parallel to the direction of motion.
- No work is done on a body moving in a circle at constant speed while constrained by a mechanical force, such as moving at constant speed in a frictionless ideal centrifuge.
- Since the force is acting parallel to the direction of motion, the angle is equal to zero and our total work is simply the force times the displacement in the x-direction.
- This means that the force is equally acting in the x and y-direction!
- Recall that both the force and direction of motion are vectors.
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Molecular Excitations
- We have effectively ignored the possible centrifugal stretching of the molecule.
- If one includes the centrifugal effects one finds that
- The centrifugal stretching reduces the spacing of the angular momentum energy levels for large values of $L$, but it stiffens the spring constant of the vibrational states.
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Rotational Collisions
- An object that has a large angular velocity ω, such as a centrifuge, also has a rather large angular momentum.
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Forces in Two Dimensions
- For example, when determining what happens when two forces act on the same object, it is necessary to know both the magnitude and the direction of both forces to calculate the result.
- In this simple one-dimensional example, without knowing the direction of the forces it is impossible to decide whether the net force is the result of adding the two force magnitudes or subtracting one from the other.
- Associating forces with vectors avoids such problems.
- Ideally, these diagrams are drawn with the angles and relative magnitudes of the force vectors preserved so that graphical vector addition can be done to determine the net force.
- Forces are resolved and added together to determine their magnitudes and the net force.
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Problem-Solving With Friction and Inclines
- Recall that the force of friction depends on both the coefficient of friction and the normal force.
- As always, the frictional force resists motion.
- If the frictional force is equal to the gravitational force the block will not slide down the incline.
- If the maximum frictional force is greater than the force of gravity, the sum of the forces is still 0.
- The force of friction can never exceed the other forces acting on it.
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Normal Forces
- The normal force comes about when an object contacts a surface; the resulting force is always perpendicular to the surface of contact.
- The person remains still because the forces due to weight and the normal force create a net force of zero on the person.
- When the elevator goes up, the normal force is actually greater than the force due to gravity.
- The second is the normal force.
- The following forces act on the mass: the weight of the mass ($m \cdot g$),the force due to friction ($F_r$),and the normal force ($F_n$).
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Centripetal Force
- A force which causes motion in a curved path is called a centripetal force (uniform circular motion is an example of centripetal force).
- A force that causes motion in a curved path is called a centripetal force.
- Uniform circular motion is an example of centripetal force in action.
- Centripetal force can also be expressed in terms of angular velocity.
- The equation for centripetal force using angular velocity is:
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Impulse
- Impulse, or change in momentum, equals the average net external force multiplied by the time this force acts.
- where F is the net force on the system, and Δt is the duration of the force.
- change in momentum equals the average net external force multiplied by the time this force acts.
- Forces are usually not constant.
- A graph of force versus time with time along the x-axis and force along the y-axis for an actual force and an equivalent effective force.