1.3 Statics Of The Body

Question 1

The study if Forces in equilibrium (bodies not accelerating) is

Answer 1

Statics

Question 2

When is a system in dynamic equilibrium?

Answer 2

When it is in equilibrium and also in motion, meaning the system is travelling at a constant velocity/ rotating at a constant rate

Question 3

In static conditions the sum of the forces F in each of the x y and z directions is

Answer 3

Zero

Question 4

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 ____

Answer 4

Static, zero

Question 5

When the net force and net torque is = 0 the system is said to

Answer 5

Be in equilibrium

Question 6

Give examples on where static equilibrium may occur

Answer 6

Question 7

When is a system said to be in stable equilibrium?

Answer 7

If it returns to equilibrium after being subject to a small displacement

Question 8

When is a system in unstable equilibrium?

Answer 8

If it doesn’t return to equilibrium after being subject to a small displacement

Question 9

When an object is wide up top but narrow on the bottom it is

Answer 9

More unstable than an object with a wider base/bottom sand narrower top

Question 10

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

Answer 10

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.

Question 11

If feet aren’t spanned and centre of mass is right over the area of the feet, what happens to the torque?

Answer 11

It’ll topple over because its unstable and unbalanced

Question 12

Stable: When the centre of mass is above the base of support (area spanned by the feet) what happens

Answer 12

The right foot= - torque
The left foot = + torque
They cancel out

Question 13

When the centre of mass is on the left or right of the toque what happens?

Answer 13

Right = both torques are positive, left = both torques are negative; therefore, the torques cannot balance and there is instability.

Question 14

We have the most stability when the centre of mass is in the

Answer 14

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)

Question 15

Define a torque

Answer 15

The tendency of a force to rotate (move in a circle) an object about its axis, fulcrum and pivot

Question 16

A torque is not a force in the Newtonian sense its a

Answer 16

Moment

Question 17

The amount of turning produced by a the force applied to a rod is dependent on the

Answer 17

Magnitude of the force and length of the rod, t=Fd unit: (Nm)

Question 18

The longer the lever arm the

Answer 18

Easier it is to rotate

Question 19

Any force that causes a counter clockwise rotation about a pivot point is said to cause a

Answer 19

Positive torque

Question 20

Any force that causes a clockwise rotation about a pivot point is said to cause a

Answer 20

Negative torque

Question 21

The equilibrium equations reduced are

Answer 21

Question 22

A system in static equilibrium = all torques balanced = no net torque, since there is no net “tendency to rotate”(torque) the system will

Answer 22

Remain motionless

Question 23

At equilibrium, the sum of clockwise and counterclockwise moments are equal, this is called the

Answer 23

Principle of moments

Question 24

All 3 lever classes are at equilibrium which means

Answer 24

Their levers effort and load forces balance each other.

Question 25

1st class levers are the least common levers of the

Answer 25

Body

Question 26

In a first class lever the Weight (load) and Muscle (effort) act on

Answer 26

opposite sides of the fulcrum in the same direction

Question 27

Examples of a first class lever are

Answer 27

Seesaw
Head atop the spinal chord
Scissors

Question 28

How come scissors are first class levers when the load and effort are moving in opposite directions?

Question 29

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

Question 30

Types of second class levers

Answer 30

Wheelbarrow
Staplers
Door/gates
Bottle openers
Nail clippers
Nut cracker
In the body: tiptoeing

Question 31

Third class levers are when the Muscle (effort) and Weight (load) of the fulcrum like the 2nd class lever, however the

Answer 31

Muscle (effort) is always in the middle, next to the fulcrum

Question 32

Third class levers are the most

Answer 32

Common levers of the body

Question 33

An example of a third class lever in the body is when the

Answer 33

Elbow is bending

Question 34

Answer 34

Remember the above

Question 35

At equilibrium in 1st class levers this rule to find the components

Answer 35

Question 36

2nd class rule

Answer 36

Question 37

3rd class lever rule

Answer 37

Question 38

True or false: torque is a type of force

Answer 38

False

Question 39

True or false equilibrium means when the net force and net torques = 0

Answer 39

True

Question 40

True or false: torque is related to the tendency to cause a rotation

Answer 40

True

Question 41

True or false:centre of gravity would not necessarily correspond/consider with the geometric centre

Answer 41

True

Question 42

The torque depends on

Answer 42

The force and lever arm

Question 43

Object is in equilibrium if the resultant force acting on it is

Answer 43

Zero

Question 44

The point where all of the weight of the object acts is called the

Answer 44

Centre of gravity