1) If an object has no force propelling it along, it will always slow down and stop because of friction (unless you're out in space where there's no friction). Friction is a force that opposes motion.

2) To travel at a steady speed, things always need a driving force to counteract the friction.

3)Friction occurs in three main ways:

a) Friction between solid surfaces which are gripping (static friction)

b)Friction between solid surfaces which are sliding past each other.

You can reduce both these types of friction by putting a lubricant like oil or grease between the surfaces. Friction between solids can often cause wear of the two surfaces in contact.

c)Resistance or Drag from fluids (liquids or Gases, e.g Air
The most important factor by far in reducing drag in fluids is keeping the shape of the object streamlined, like sports cars or boat hulls. Lorries and caravans have "deflectors" on them to make them more streamlines and reduce drag. Roof boxes on cars spoil the streamlined shape and so slow them down. For a given thrust , the higher the Drag, the lower the top speed of the car.The opposite extreme to a sports car is a parachute which is about as high drag as you can get-which is. of course, the whole idea . In a FLUID, FRICTION always INCREASES as the SPEED INCREASES.

	Erstellt von ThulasyA97 vor etwa 11 Jahre

physics Notiz am Forces and motion : D-T and V-T graphs, erstellt von ThulasyA97 am 19/04/2013.