1.3 Statics Of The Body Flashcards
The study if Forces in equilibrium (bodies not accelerating) is
Statics
When is a system in dynamic equilibrium?
When it is in equilibrium and also in motion, meaning the system is travelling at a constant velocity/ rotating at a constant rate
In static conditions the sum of the forces F in each of the x y and z directions is
Zero
Each torque can also be resolved into components in the x,y,x direction. In _____ condition, the torques about the x,y,z axes also each sum to ____
Static, zero
When the net force and net torque is = 0 the system is said to
Be in equilibrium
Give examples on where static equilibrium may occur
When is a system said to be in stable equilibrium?
If it returns to equilibrium after being subject to a small displacement
When is a system in unstable equilibrium?
If it doesn’t return to equilibrium after being subject to a small displacement
When an object is wide up top but narrow on the bottom it is
More unstable than an object with a wider base/bottom sand narrower top
Stability is essential during standing. For stability while standing the centre of mass but be over the area spanned by the feet. What does this mean
A vertical line passing through the centre of mass passes in this area of the base of support. This makes sense because the wide base = more stability than if we were to stand on 1 leg or our heads.
If feet aren’t spanned and centre of mass is right over the area of the feet, what happens to the torque?
It’ll topple over because its unstable and unbalanced
Stable: When the centre of mass is above the base of support (area spanned by the feet) what happens
The right foot= - torque
The left foot = + torque
They cancel out
When the centre of mass is on the left or right of the toque what happens?
Right = both torques are positive, left = both torques are negative; therefore, the torques cannot balance and there is instability.
We have the most stability when the centre of mass is in the
Centre of the base of support, the term centre of gravity can be used instead of centre of mass when stability is there (when it is in the centre)
Define a torque
The tendency of a force to rotate (move in a circle) an object about its axis, fulcrum and pivot
A torque is not a force in the Newtonian sense its a
Moment
The amount of turning produced by a the force applied to a rod is dependent on the
Magnitude of the force and length of the rod, t=Fd unit: (Nm)
The longer the lever arm the
Easier it is to rotate
Any force that causes a counter clockwise rotation about a pivot point is said to cause a
Positive torque
Any force that causes a clockwise rotation about a pivot point is said to cause a
Negative torque
The equilibrium equations reduced are
A system in static equilibrium = all torques balanced = no net torque, since there is no net “tendency to rotate”(torque) the system will
Remain motionless
At equilibrium, the sum of clockwise and counterclockwise moments are equal, this is called the
Principle of moments
All 3 lever classes are at equilibrium which means
Their levers effort and load forces balance each other.
1st class levers are the least common levers of the
Body
In a first class lever the Weight (load) and Muscle (effort) act on
opposite sides of the fulcrum in the same direction
Examples of a first class lever are
Seesaw
Head atop the spinal chord
Scissors
How come scissors are first class levers when the load and effort are moving in opposite directions?
A second class lever when the Muscle (effort) and Weight (load) act on the same side of the fulcrum with the Weight (load) always next to the fulcrum - in the middle
Types of second class levers
Wheelbarrow
Staplers
Door/gates
Bottle openers
Nail clippers
Nut cracker
In the body: tiptoeing
Third class levers are when the Muscle (effort) and Weight (load) of the fulcrum like the 2nd class lever, however the
Muscle (effort) is always in the middle, next to the fulcrum
Third class levers are the most
Common levers of the body
An example of a third class lever in the body is when the
Elbow is bending
Remember the above
At equilibrium in 1st class levers this rule to find the components
2nd class rule
3rd class lever rule
True or false: torque is a type of force
False
True or false equilibrium means when the net force and net torques = 0
True
True or false: torque is related to the tendency to cause a rotation
True
True or false:centre of gravity would not necessarily correspond/consider with the geometric centre
True
The torque depends on
The force and lever arm
Object is in equilibrium if the resultant force acting on it is
Zero
The point where all of the weight of the object acts is called the
Centre of gravity
