Week 5 - Levers & Torque Flashcards
1
Q
Define Lever
A
a rigid bar that is rotated about a fixed point or axis (called a fulcrum)
2
Q
List components of a lever (3 points)
A
- Effort force (the place where force is applied)
- Resistance force (the place where the resistance acts)
- Fulcrum (pivot point/ axis of rotation)
3
Q
Describe moment arms (3 points)
A
- M.A (moment arm) = Perpendicular distance from the line of action to the axis of rotation (m)
- Effort arms: Perpendicular distance from the line of the effort force to the axis of rotation/ fulcrum
- Resistance arms: Perpendicular distance from the line of the resistance force to the axis of rotation/ fulcrum
4
Q
Describe mechanical advantage (6 points)
A
- The mechanical effectiveness of a lever can be evaluated by calculating its mechanical advantage (MA).
- Formula: MA= effort arm/resistance arm
- If the effort arm is greater than the resistance arm, then MA will be greater than 1. This is a mechanical advantage.
- Magnitude of the force required to move resistance is less than the magnitude of the resistance.
- If the effort arm is less than the resistance arm, then MA will be less than 1. This is a mechanical disadvantage.
- Must apply greater force than resistance to create motion
5
Q
Describe classes of levers (7 points)
A
- 3 different classes of levers, depending on the structure
- 1st class Levers: The effort and resistance force are on opposite sides of the fulcrum.
- E.g. See-saw, crowbar, hammer pulling out a nail.
- 2nd class Levers: The effort and resistance force are on the same side of the fulcrum. The resistance force is between the fulcrum and effort.
- E.g. Wheelbarrow and Nutcracker
- 3rd class Levers: The effort and resistance force are on the same side of the fulcrum. The effort force is between the fulcrum and resistance.
- E.g. Shovel, Fishing rod cast and most joints in the human body.
6
Q
Describe functions of levers (2 points)
A
- To increase the effect of a force (EA>RA)
- To increase the speed at the end of the lever (EA<RA)
7
Q
Describe Levers in Human Movement (5 points)
A
- Musculoskeletal lever systems have a mechanical disadvantage in force.
- Muscles (the foot arm) attach so closely to the joint (the fulcrum) that they are at a mechanical disadvantage.
- The advantage of this in the speed of movement, especially 3rd class levers.
- This speed advantage has implications for many sporting activities including throwing and striking.
- The negative is that muscles need to apply large force to overcome the mechanical disadvantage.
8
Q
Describe torque (11 points)
A
- Torque is the turning effect caused by a force. Also known as a moment of force or a moment.
- Three types of forces involved torque:
- Centric force
- Eccentric force
- Force couple
- Three components:
- Specified axis of rotation (where is the rotation going to occur from)
- Magnitude (F x ma). Units: Newtons x meters (N.m)
- Direction (sense) of torque:
- Clockwise = negative
- Counter clockwise = positive
9
Q
Describe the types of forces involved in torque (3 points)
A
- Centric force: A force acting through the centre of gravity. Causes liner motion
- Eccentric force: Line of action does not pass through the axis of rotation. Often causes rotation and small amount of linear motion
- Force Couple: Two equal & opposite parallel forces. Causes only rotation
10
Q
Describe Equilibrium (5 points)
A
- Can be defined as the state in which acceleration is zero (net force is zero)
- ΣF = m x a
- If a = 0 the ΣF = 0
- Static equilibrium: when velocity is zero
- Dynamic equilibrium: when velocity is constant and other than zero
11
Q
What affects torque? (5 points)
A
- Torque is the turning effect of a force
- Influenced by the size of the force and the line of action of that force
- Torque = F x M.A (N.m) where:
- F = magnitude of force
- M.A (moment arm) = perpendicular distance from the line of action to the axis of rotation (m)
12
Q
Provide everyday examples of torque (6 points)
A
- Book pages
- Steering wheel
- Door handles
- Screw drivers
- Shovels
- Pegs
13
Q
How does changing the line of action affect the torque? (7 points)
A
- If the force is not directly parallel (so is moving at an angle), then the moment becomes more difficult to calculate
- For example, when pushing open a door, is the force applied is perpendicular to door, then the moment arm is whatever length between the location of the force and the axel. This is easy to calculate.
- However, is the force is being applied at an angle, the length of the moment arm is less clear due to the line of action being different
- Trigonometry is used to calculate moment arm,
- Firstly, the degree of the angle and the amount of force applied at that angle must be identified.
- Then trigonometry can be used to calculate the perpendicular line of force.
- Finally, the moment arm can be measured as normal
14
Q
Provide sports examples of torque (5 points)
A
- Rowing, kayaking and canoeing
- Cycling
- Golf, tennis and cricket
- Gymnastics and diving
- Wrestling
15
Q
Describe muscle torque (5 points)
A
- Muscle applies force by pulling
- Line of action is usually indicated by the direction of the tendons
- Muscle crosses a joint or joints
- Muscle has a moment arm
- Muscle creates torque at the joint
