Chapter 8 Torques and Moments of Force Maintaining
- Slides: 48
Chapter 8 Torques and Moments of Force: Maintaining Equilibrium or Changing Angular Motion
To this juncture n Analysis focused on linear motion (translation) – kinematics: position, change of position, rate of change of position, acceleration – kinetics: Newton’s 3 laws of linear motion » F = ma » Ft = mv
What about rotation? n All points on a body or object move in circles (or parts of circles) about the same fixed central line or axis – body spin around an axis (real or imaginary) Force ==> linear motion n ? ? ? ==> angular motion n
What about rotation? n All points on a body or object move in circles (or parts of circles) about the same fixed central line or axis – body spin around an axis (real or imaginary) Force ==> linear motion n Torque ==> angular motion n – moment of force – moment
Characteristics of a Force
Characteristics of a Force n. Magnitude
Characteristics of a Force n. Magnitude n. Direction
Characteristics of a Force n. Magnitude n. Direction n. Point of Application n. Line of Action
Line of action relative to axis of rotation n Centric force – line of action passes through the axis of rotation – tends to cause translation
Line of action relative to axis of rotation Centric force n Eccentric force n – line of action does not pass through the axis of rotation – tends to cause translation and rotation
Line of action relative to axis of rotation Centric force n Eccentric force n Force couple n – two eccentric forces – tends to cause rotation
Torque http: //www. tri-c. cc. oh. us/metro/faculty/gram/web/torque. htm n Definition – the turning effect of a force – the tendency of a force to cause rotation What factors affect the tendency of the force to cause rotation? ? ?
Torque http: //www. tri-c. cc. oh. us/metro/faculty/gram/web/torque. htm n Definition – the turning effect of a force – the tendency of a force to cause rotation What factors affect the tendency of the force to cause rotation? ? ? Why my pinky can whip your football team.
Torque n Definition – the turning effect of a force – the tendency of a force to cause rotation T=Fxr T = torque F = force (magnitude & direction) r = moment arm (MA)
Moment Arm (lever arm) Perpendicular distance from line of action of a force to a specified axis of rotation (fulcrum, pivot point)
Moment Arm (lever arm) Perpendicular distance from line of action of a force to a specified axis of rotation
Moment Arm (lever arm) Perpendicular distance from line of action of a force to a specified axis of rotation Axis
Moment Arm (lever arm) Perpendicular distance from line of action of a force to a specified axis of rotation Moment Arm (r)
Characteristics of a Force Note how changing the line of action of a force may change the sense of the torque Moment Arm (r)
Effect of changing the line of action of force
To describe a torque Specified axis of rotation n Torque magnitude (F x r) n – units: Newtons x meters (Nm) – foot x pound (ft-lb) n Direction (sense) of the torque – clockwise (-) – counterclockwise (+)
Examples of Torque
Examples of Torque Show the moment arm and identify the sense for each force on each figure
Examples of Torque Calculate torque created in each figure
Sculling: offsetting torques to create translation Are all three designs equal in net torque created at the stern? ?
ADLs must consider torque for safety and convenience Medicine caps must be removable by the disadvantaged, but inoperable by kids. Click on the picture to go to a website with more information.
Muscle Names
Muscle Torque n Muscle applies force by ? ? ?
Muscle Torque n Muscle applies force by pulling
Muscle Torque n Muscle applies force by pulling n Muscle crosses a joint or joints – brachialis and biceps brachii – soleus and gastrocnemius – other examples? ?
Muscle Torque n Muscle applies force by pulling n Muscle crosses a joint or joints n Muscle has a moment arm – eg palpate the biceps brachii and flex elbow » next three slides
Elbow at 90 o of flexion
Elbow at 135 o of flexion
Elbow at 45 o of flexion
Question posed in a Physical Therapist Assistant Class Is it still a moment arm if the muscle inserts on the leg? Reported by Kris Green, BS ‘ 99
Muscle Torque n Muscle applies force by pulling n Muscle crosses a joint or joints n Muscle has a moment arm n Muscle creates torque at the joint – muscle is a torque generator » Bob Norman (1975)
Game Day Draw the Resistance Torque
Strength training and torque Biceps Curl n Muscle as torque generator – moment arm changes through ROM – muscle’s ability to create force changes through ROM n External forces as torque generators – segment weight – handheld weight (dumbbell) » moment arms change through ROM
Strength training and torque
Strength Training Machines
So our answer is: Why could I control the two big guys with only my pinky? Because, ….
Calculate Extensor Muscle Forces: P (hand held load) = 90 N W (HAT weight) = 80 N Moment Arms Lw = 25 cm Lp = 60 cm Lm = 5 cm
Moment arm at the knee joint n Go to and read Click for knee website the Web site to see how the moment arm at the knee is affected by knee joint angle.
Ankle moment and standing n Go to and read Interesting Web Site on Balance the Web site to see how the moment arm of the ground reaction force acts at the ankle joint.
Forces and Torques in Equilibrium n Static Equilibrium – sum of forces on the body = 0 » F = 0 – sum of torques on the body = 0 » T = 0
Demonstration of Net Torque Balancing Pennies
Solving for Net Torque Mathematically Wt = -p (weight of a penny) r = distance (inches) from axis What is force on ruler from fulcrum? ? ?
Solving for Net Torque Mathematically Wt = -p (weight of a penny) r = distance (inches) from axis What is force on ruler from fulcrum? ? ? T = 0 (static equilibrium)
- Signos del torque
- Calculo
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- Building and maintaining a website
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- Maintaining a healthy body composition and body image
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- Hooke's law vector form
- Normal force diagram
- How to maintain deliverance
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- Class maintaining prefixes
- Potential tension between maintaining confidentiality
- Maintaining a teachable spirit
- Maintaining a website
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- Interpersonal accord and conformity
- Maintaining effective partnerships
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- Maintaining student privacy
- Maintaining
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- Contact vs noncontact forces
- What force provides centripetal force
- Long range force
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- The ratio of resistance force to effort force