buoyant force

Examples of buoyant force in the following topics:

• Buoyancy and Archimedes' Principle

  • The buoyant force on an object can be calculated using the Archimedes principle.
  • What creates this buoyant force?
  • The result is a net upward force (a buoyant force) on any object in any fluid.
  • If the buoyant force is less than the object's weight, the object will sink.
  • The buoyant force is a result of pressure exerted by the fluid.

• Flotation

  • But the Archimedes principle states that the buoyant force is the weight of the fluid displaced.
  • Thus, only in the special case of floating does the buoyant force acting on an object equal the object's weight.
  • The deeper the iron bowl is immersed, the more water it displaces, and the greater the buoyant force acting on it.
  • When the buoyant force equals one ton, it will sink no further.
  • The buoyant force, which equals the weight of the fluid displaced, is thus greater than the weight of the object.

• Static Equilibrium

  • Next, the forces acting on this region within the medium are taken into account.
  • This force which counteracts the weight of a region or object within a static fluid is called the buoyant force (or buoyancy).
  • As previously discussed, there are two downward acting forces, one being the weight of the object and the other being the force exerted by the pressure from the fluid above the object.
  • At the same time, there is an upwards force exerted by the pressure from the fluid below the object, which includes the buoyant force. shows how the calculation of the forces acting on a stationary object within a static fluid would change from those presented in if an object having a density ρS different from that of the fluid medium is surrounded by the fluid.
  • The appearance of a buoyant force in static fluids is due to the fact that pressure within the fluid changes as depth changes.

• Complete Submersion

  • The buoyancy force on a completely submerged object of volume is $F_B = V \rho g$ .
  • In the previous section, we calculated the buoyancy force on a cylinder (shown in ) by considering the force exerted on each of the cylinder's sides.
  • Now, we'll calculate this force using Archimedes' principle.
  • The buoyancy force on an airship is due to the air in which it is immersed.
  • Therefore, the net buoyant force is always upwards.

• Applications of Newton's Laws

  • Net force affects the motion, postion and/or shape of objects (some important and commonly used forces are friction, drag and deformation).
  • Another interesting force in everyday life is the force of drag on an object when it is moving in a fluid (either gas or liquid).
  • Like friction, the force of drag is a force that resists motion.
  • We see an illustrated example of drag force in.
  • It omits the two vertical forces—the weight of the barge and the buoyant force of the water supporting it cancel and are not shown.

• Humidity, Evaporation, and Boiling

  • For the molecules to evaporate, they must be located near the surface, be moving in the proper direction, and have sufficient kinetic energy to overcome liquid-phase intermolecular forces.
  • The bubble grows in size and thereby increases the buoyant force.

• Convection

  • Natural convection is driven by buoyant forces: hot air rises because density decreases as temperature increases.
  • Water vapor carried in by convection condenses, releasing tremendous amounts of energy, and this energy allows air to become more buoyant (warmer than its surroundings) and rise.

• Thermal Stresses

  • Hot air rises because its volume increases, which causes the hot air's density to be smaller than the density of surrounding air, causing a buoyant (upward) force on the hot air.
  • Forces and pressures created by thermal stress can be quite large.

• Geomagnetism

  • A magnetic field is generated by a feedback loop: Current loops generate magnetic fields (Ampère's law); a changing magnetic field generates an electric field (Faraday's law); and the electric and magnetic fields exert a force on the charges that are flowing in currents (the Lorentz force).
  • The temperature increases toward the center of Earth, and the higher temperature of the fluid lower down makes it buoyant.
  • A schematic illustrating the relationship between motion of conducting fluid, organized into rolls by the Coriolis force, and the magnetic field the motion generates.

• 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.