(non-)contact and resultant forces

• vectors have...

  magnitude and direction
• magnitude

  distance or quantity
• direction

  the location of something relative to something else
• vectors are usually represented by an...

  aarow - the length of the arrow shows the magnitude and the direction of the arrow shows the direction of the quantity
• vector quantities examples

  force, velocity. displacement, acceleration, momentum
• what physical quantites only have magnitude and no direction?

  scalar quantities
• scalar quantities examples

  speed, distance, mass, energy, temperature, time
• forces can be ... or ...

  contact, non-contact
• force

  a push or pull on an object that is caused by it ineracting with something
• contact force

  a force that requires two pieces of matter to touch
• contact force examples

  friction, air resistance, tension in ropes
• non-contact force

  a force that one object can apply to another object without touching it
• non-contact force examples

  magnetic force, gravitational force, electrostatic force
• scale diagram

  a way of working out the resultant forces or component forces by drawing a diagram where the lengths of arrows represent the sizes of the forces.
• scale diagram example

  
• how can you tell if a set of forces are balanced using a scale diagram?

  if all the the arrows representing forces are connected tip to toe and forming a closed loop, the forces are balanced
• balanced forces scale diagram example

  
• when two object interact, there is a ... produced on ... objects

  force, both
• interaction pair

  a pair of forces that are equal in strength and opposite in direction that act on the two interaction objects
• gravitational force

  an attractive force that acts between any two objects
• gravity attracts ... masses

  all
• effects of gravity

  - on the surface of a panet, it makes all things fall towards the ground

  - it gives everything weight
• weight

  a measure of the force of gravity on an object
• mass

  the amount of matter in an object
• mass and weight are ...

  directly proportional
• increasing the mass of an object ... its weight

  increases
• doubling the mass of an object ... its weight

  doubles
• weight (N) =

  mass (kg) x gravitational field strength (N/kg)
• weight formula

  W=mg
• weight formula triangle

  
• difference between weight and mass

  - mass is the amount of matter in an object while weight is the measure of the gravitational pull on an object

  - weight varies from place to place while mass remains the same

  - mass is not a force measured in kilograms with a mass balance

  - weight is a force measured in newtons with a newtonmeter

  - mass is a scalar quantity, weight is a vector quantity
• centre of mass

  the point at which the body is balanced in all directions
• centre of gravity

  the point at which the entire weight of an object can be considered to act
• how can you make an object more stable?

  - lower centre of mass

  - widen the support base
• how do you find the centre of mass?

  suspend the object from two locations and to drop plumb lines from the suspension points - the intersection of the two lines is the center of mass
• gravitational field strength

  the measure of the intensity of the gravitational field that has mass as a source and attracts other masses
• gravitation field strength varies with ...

  location
• gravitational field strength is stronger the ... you are to the mass causing the field

  closer
• gravitational field strength is stronger for ... masses

  larger
• an object has the ... mass whether it's on the Earth or on the Moon, but it's weight will be ...

  same, different