friction, drag and resistance

• friction is always there to...


  slow things down
• friction


  a force that opposes motion between two surfaces that are in contact
• what is friction caused by?

  the interactions between the tiny bumps on surfaces as they rub against each other - the bumps on each surface bend and exert a force on each other making it hard for the surfaces to slip over each other
• friction always acts in the ... direction to movement

  opposite
• if a object as no force propelling is along, it will always...

  slow down and stop
• to travel at a steady speed, the driving force needs to ... the frictional forces

  balance
• drag


  the resistance you get in a fluid (a gas or a liquid) against direction of movement
• what is the most important factor in reducing drag?

  keeping the shape of the object streamlined - this is where the object is designed to allow fluid to flow easily across it, reducing drag
• air resistance is a type of...

  drag - it's a frictional force produced by the air acting on a moving object
• what is drag caused by?

  by the collision of the air molecules with the surface of the object that is passing through it
• drag increases as speed...


  increases
• why does drag increase as speed increases?

  as speed increases so too does the frequency of the collision of air molecules with the object, this results in an increase in drag
• objects falling through fluids reach a...

  terminal velocity
• when falling objects first set off, the force of gravity is much ... than the frictional force slowing them down

  more
• the force of gravity on a falling object being bigger than the frictional force makes the object...

  accelerate
• As the speed of a falling object increases...

  air resistance increases
• the air resistance on a falling object gradually ... the acceleration

  reduces
• the air resistance on a falling object reducing the acceleration does so until eventually...


  the frictional force is equal to the acceleration force (so the resultant force is zero)
• the resultant force on a falling object being zero means..

  it will have reached its maximum speed (or terminal velocity) and fall at a steady speed
• terminal velocity


  the constant and greatest velocity a falling object can achieve
• terminal velocity depends on...

  the object's shape, area and mass
• the accelerating force acting on all falling objects is...

  gravity, and it would make them all fall at the same rate (if it weren't for air resistance)
• on the moon (where there is no air) hammers and feathers dropped simultaneously will hit the ground...

  together
• on Earth, air resistance causes things to fall at...


  different speeds
• the terminal velocity of any object is determined by...

  its drag in comparison to its weight
• the frictional force of a falling object depends on its...


  shape and area
• a force is needed to...

  change motion