Chapter 4 Forces, Density & Pressure Flashcards
a couple has a pure turning effect. Why?
- because a single force will tend to make an object accelerate (unless another force balances it)
- where a couple is a pair of equal, opposite forces = will not make object accelerate.
- The turning effect, well force is determined by its torque
balanced or unbalanced
- check whether an object remains balanced or start to rotate - calulate an unknown force or distance if we know the object is balanced
centre of gravity
the point where the entire weight of an object appear to act
finding moment of force (method 1)
-draw perpendicular line from the pivot to the line of the force - find the distance from pivot. -find force -calculate moment of force (F1 x x2) -we see that: x2 = d sin(angle) hense: moment = F2 x d sin(angle) x2 = distance from pivot to 90 degree of F2 line(figure 4.17)
find the moment (method 2)
calculate the component of F2 that is at 90 to the lever.
-this is F2 sin(angle).multiply by d moment = F2 sin(angle) x d
For an object to be in equilibrium two conditions must be met?
-resultant force acting on the object is zero -the resultant moment is zero
how to resolve a force F into its horizontal and vertical components
horizontal component of F, Fx = F cos(angle) vertical component of F, Fy = F sin(angle)
moment of a force Def
of a force about a point is the product of a force and perpendicular distance from the line of action of the force to the point.
moment of force =
force x distance from pivot depends on two forces: -magnitude of force -perpendicular distance of the force from pivot Torque=FD Torque= Nm Force = F Distance= the perpendicular force from pivot (meters)
principle of moments
the sum of clockwise moments about a point is equal to the sum of the anticlockwise moments about the same point provided the body is in equilibrium
resolving
to split a vector (such as force) into two vectors at right angles
to form a couple, the two forces must be:
-equal in magnitude -parrel, but opposite in direction -separated by a distance
torque def
the product of one of the forces and the perpendicular distance between the forces. (the turning effect or moment of a couple)
torque of a couple =
one of the forces x separation of forces Torque about O = (F x OA) + (F x OB) O = FD
two forces at a right angle (drawn) (Combining vectors)
-first draw a horizontal arrow to represent the Force -Next, starting from the end of this arrow, draw the second arrow in the irection its effecting -now, draw a line from the start to the end of the second arrow ( represent resultant force ) -resulatant force = scaled diagram or by calculation (phytagorus theorm)