Upthrust

• Upthrust:

  • When an object is submerged in fluid, the pressure exerts a force in every direction
  • Pressure increases with depth so the force on the bottom of the object is larger than the force on the top of the object
  • This causes a resultant force upwards, known as upthrust
• Upthrust is equal to the weight of fluid that has been displaced by the object
• This means the forces balance and the object floats
• If an objects weight is more than the up thrust, the object sinks
• An object floating depends on its density, if an object is less dense it displaces an equal volume of fluid to its weight. This means it is completely submerged
• A denser object means it is unable to displace enough fluid equal to its weight so it sinks
• Atmospheric pressure decreases with height. As altitude increases, pressure decreases as the atmosphere is less dense