Physics Mechanics flashcards

Vectors

any physical quantity that has a direction, as well as a magnitude

• Represented with a line and an arrow 

  • Length of line indicates magnitude

  • Arrow indicates direction

Scalar

quantity which only has magnitude

• Represented using a line

  • Length of line indicates magnitude

Rules for adding vectors

• Vectors in same direction have the magnitudes added together

• Vectors in opposite directions have the magnitudes subtracted

• If the object does not move, no work is done

• Work done must be in same direction as the force

Equilibrium

no net force or moment (resultant force) acts on it

• Forces and moments are balanced

• resultant force = 0

Equilibrant vector

resultant vector in opposite direction

For a system to be in equilibrium

• Sum of x components = 0

• Sum of vertical components or forces = 0

Torque

moment of a force

Centre of gravity

where the entire weight of the object seems to act 

• Point through which a single force has no turning effect on the body

Centre of mass

where the entire mass of an object seems to be concentrated

• Point through which a single force has no turning effect on the body

• Uniform - evenly distributed 

• In uniform gravitational field the centre of mass is the same place as the centre of gravity

• Located at the point of symmetry in symmetrical objects with uniform density

Principle of moments (for a body in equilibrium)

Total clockwise moment = total anticlockwise moment

Stability

 An object is stable when its centre of mass lies above its base

• The wider base an object has, the lower its centre of mass and it is more stable

• The narrower base an object has, the higher its centre of mass and the object is more likely to topple over if pushed