Unit 6 Force and Levers Flashcards
Explain the difference between Newton’s Three Laws of Motion. Give an example of each law.
Law of Inertia: An object at rest tends to stay at rest, and an object in motion tends to stay in motion, unless an external force is applied to it. Example: riding in a car
The law of inertia is a major factor in whiplash. A force is needed to overcome inertia and cause the object to move, to stop the object from moving or to change its direction
Law of Acceleration: Acceleration = any change in the velocity of an object. The amount of acceleration depends on the strength of the force applied to the object. Force is needed to change direction of an object. Mass = the amount of matter in an object. Example: assuming a constant force, roll a light soccer ball and it will accelerate faster than a heavier bowling ball
Law of Action-Reaction: For every action there is an equal and opposite reaction. The strength of the action = the strength of the reaction, in the opposite direction. Example: jumping on a trampoline
Explain the equation: a = F/m (acceleration = force/mass)
Acceleration is inversely proportional to the mass of an object. Assuming a constant force, this means that a heavier object will accelerate slower and a lighter object will accelerate faster
Describe the difference between internal and external forces on our bodies. Give an example of each.
Internal forces are forces that act on our body from structures within our body such as muscular contractions. External forces are forces that act on our body from outside our body such as gravity, friction or applying an external resistance.
Define the following terms: torque, moment arm, stabilizing force and angular force. Give an example of each.
Torque (also called moment of force) = the ability of force to produce rotation around an axis (a rotary force). Example: the amount of force, or torque, needed for biceps to flex the elbow and cause rotation around the elbow joint axis
Moment Arm = is the perpendicular distance between the axis of rotation (joint axis) and the line of force or line of pull of a muscle. Example: the distance between the axis of rotation of the elbow joint and the insertion of biceps tendon on to the radius
Stabilizing Force = nearly all the force generated by the muscle is directed back into the joint to stabilize the joint and pull the joints together (increase in congruency). Example: a stabilizing force occurs at the elbow joint when the elbow is extended
Angular Force = nearly all the force generated by the muscle is directed at rotating the joint; this is a movement force (less congruent joint). Example: when the elbow is at 90 degrees flexion, there is an angular force that will assist the elbow joint to rotate (into flexion or extension)
What are the 3 classes of levers and give an anatomical example of each class of lever.
First Class Lever = axis is between force and resistance. Example: neck flexion/extension where weight of head is the resistance; cervical muscle is the force; cervical vertebra is the axis
Second Class Lever = resistance is located between force and axis. Example: heel raise where tibia and body weight is the resistance; plantar flexor muscles is the force; MTP joint is the axis (not the talocrural ankle joint because the axis is located away from the resistance and force in a second class lever (F R A).
Third Class Lever = force is located between resistance and axis. Example: biceps elbow flexion where weight of the forearm is the resistance; biceps is the force and the elbow joint is the axis
Which lever is best designed for balance?
First Class Levers
Which lever is found most often in our bodies and why?
Third class levers which are designed for distance (ROM). ROM or distance gained is more functional than advantage gained from power or balance
Explain the importance of mechanical advantage with respect to levers and give an example of mechanical advantage in the body.
- the efficiency of a lever when a smaller effort to overcome a large resistance.
- important in rehabilitation when strengthening a weakened muscle by decrease the RA and increasing the FA to move parts easier by allowing less energy to gain strength.
- For example: placing a cuffed weight around a client’s forearm will decrease the resistance arm and will require less force to perform elbow flexion exercise.
