Physics uCc Flashcards
Explain biomechanics
What is mechanics
State the types
Explain them
Study of mechanics as it relates to the functional and anatomical analysis of biological systems and especially humans
It is necessary to study the body’s mechanical characteristics and principles to understand its movements
Mechanics is the study of physical actions of forces
It’s divided into statics and dynamics
Statics is the study of systems that are in a constant state of motion whether at rest with no motion or moving at a constant velocity with no acceleration
Static’s involve all forces acting on the body being in balance resulting in the body being in equilibrium
Dynamics is the study of systems in motion with acceleration
A system in acceleration is unbalanced due to unequal forces acting in the body
Kinematic sis the description of motion and includes consideration of time ,displacement,velocity,acceleration and space factors of a systems motion
Kinetics is the study of forces associated with motion of a body
Explain mechanical advantage under types of machines found in the body
State the four ways machine functions
Which machine types are not found in the body
The mechanical advantage provided by machines enables us to apply a relatively small force, or effort, to move a much greater resistance or to move one point of an object a relatively small distance to result in a relatively large amount of movement of another point of the same object. We can determine mechanical advantage by dividing the load by the effort.
Load effort or load divided by effort.
Ideally using a relatively small force or effort to move a much greater resistance
The musculoskeletal system may be thought of as series of simple machines
-machines used to increase mechanical advantage
Machines function in four ways:
1. To balance multiple forces
2. To enhance force in an attempt to reduce the
total force needed to overcome a resistance
3. To enhance range of motion and speed of move- ment so that resistance can be moved farther or faster than the applied force
4. To alter the resulting direction of the applied force
Simple machines are the lever, wheel and axle, pulley, inclined plane, screw, and wedge. The arrangement of the musculoskeletal system provides three types of machines in producing movement: levers(most common), wheel/axles, and pulleys. Each of these involves a balancing of rotational forces about an axis. The lever is the most common form of simple machine found in the human body.
Not found in the body:
Inclined plane
Screw
Wedge
How does human movement occur
What is a lever
What is an axis
In the body,what represents the bars,axes and what applies the force?
What points determine the types of lever and for which motion it’s best suited
system of levers, but this is actu- ally the case. Human movement occurs through the organized use of a system of levers. While the anatomical levers of the body cannot be changed, when the system is properly understood they can be used more efficiently to maximize the muscular efforts of the body.
A lever is defined as a rigid bar that turns about an axis of rotation, or fulcrum. The axis is the point of rotation about which the lever moves. The lever rotates about the axis as a result of force (some- times referred to as effort, E ) being applied to it to cause its movement against a resistance (sometimes referred to as load or weight). In the body, the bones represent the bars, the joints are the axes, and the muscles contract to apply the force. The amount of resistance can vary from maximal to minimal. In fact, the bones themselves or the weight of the body segment may be the only resistance applied. All lever systems have each of these three components in one of three possible arrangements.
The arrangement or location of three points in relation to one another determines the type of lever and the application for which it is best suited. These points are the axis, the point of force application (usually the muscle insertion), and the point of resistance application (sometimes the center of gravity of the lever and sometimes the location of an external resistance).
Explain the types of levers
How is mechanical advantage of levers determined
When the axis (A) is placed anywhere between the force (F) and the resistance (R), a first-class lever is produced (Fig. 3.1). In second-class levers, the resistance is somewhere between the axis and the force (Fig. 3.2). When the force is placed somewhere between the axis and the resistance, a third-class lever is created
Mechanical advantage = resistance / force
Mechanical advantage = length of force arm / length of resistance arm
First class levers
Typical examples of a first-class lever are the crowbar, the seesaw, pliers, oars, and the triceps in overhead elbow extension. In the body an example is when the triceps applies the force to the olec- ranon (F) in extending the nonsupported forearm (R) at the elbow (A). Other examples are when the agonist and antagonist muscle groups on either side of a joint axis are contracting simultaneously, with the agonist producing the force and the antagonist supplying the resistance. Head balanced on neck in gelding and extendjng A first-class lever (see Fig. 3.1) is designed basically to produce balanced movements when the axis is midway between the force and the resistance (e.g., a see- saw). When the axis is close to the force, the lever produces speed and range of motion (e.g., the tri- ceps in elbow extension). When the axis is close to the resistance, the lever produces force motion (e.g., a crowbar). In applying the principle of levers to the body, it is important to remember that the force is applied where muscle inserts in bone, not in the belly of the muscle. For example, in elbow extension with the shoulder fully flexed and the arm beside the ear, the triceps applies the force to the olecranon of the ulna behind the axis of the elbow joint in extending the non supported forearm at the elbow. As the applied force exceeds the amount of forearm resistance, the elbow extends.
The type of lever may be changed for a given joint and muscle depending on whether the body segment is in contact with a surface such as a floor or wall. For example, we have demonstrated that the triceps in elbow extension is a first-class lever with the hand free in space and the arm pushed away from the body. If the hand is placed in con- tact with the floor, as in performing a push-up to push the body away from the floor, the same muscle action at this joint now changes the lever to second class, because the axis is at the hand and the resistance is the body weight at the elbow joint.
What do Second class levers produce and give examples What do third class levers produce and give examples in the body Which part of the body is a true third class lever
Second-class levers A second-class lever (see Fig. 3.2) is designed to produce force movements, since a large resistance can be moved by a relatively small force. Examples of second-class levers include a bottle opener, a wheelbarrow, and a nutcracker. We have just noted the example of the triceps extending the elbow in a push-up. A similar example of a second-class lever in the body is plantar flexion of the ankle to raise the body on the toes. The ball (A) of the foot serves as the axis of rotation as the ankle plantar flexors apply force to the calcaneus (F) to lift the resistance of the body at the tibiofibular articulation (R) with the talus. Opening the mouth against resistance provides another example of a second-class lever. There are relatively few other examples of second- class levers in the body
Third-class levers
Third-class levers (see Fig. 3.3), with the force being applied between the axis and the resis- tance, are designed to produce speed and range of motion. Most of the levers in the human body are of this type, which requires a great deal of force to
move even a small resistance. Examples include a catapult, a screen door operated by a short spring, and the application of lifting force to a shovel han- dle with the lower hand while the upper hand on the shovel handle serves as the axis of rotation. The biceps brachii is a typical example in the body. Using the elbow joint (A) as the axis, the biceps brachii applies force at its insertion on the radial tuberosity (F) to rotate the forearm up, with its cen- ter of gravity (R) serving as the point of resistance application.
The brachialis is an example of true third-class leverage. It pulls on the ulna just below the elbow, and, since the ulna cannot rotate, the pull is direct and true. The biceps brachii, on the other hand, supinates the forearm (applying the rotational force of a first-class lever as in a wheel and axle to the radius) as it flexes, so the third-class leverage applies to flexion only.
Other examples include the hamstrings con- tracting to flex the leg at the knee in a standing position and the iliopsoas being used to flex the thigh at the hip.
Factors in use o
What are the are the factors in the use of anatomical levers
What is torque as a factor
And eccentric force
What is resistance arm
Explain the inverse relationship between the length of two lever arms
Lever equation is force x force of arm = resistance x resistance of arm
Our anatomical leverage system can be used to gain a mechanical advantage that will improve simple or complex physical movements. Some individuals unconsciously develop habits of using human levers properly, but frequently this is not the case.
Torque and length of lever arms
To understand the leverage system, the concept of torque must be understood. Torque, or moment of force, is the turning effect of an eccentric force. Eccentric force is a force that is applied off cen- ter or in a direction not in line with the center of rotation of an object with a fixed axis. In objects without a fixed axis, it is an applied force that is not in line with the object’s center of gravity; for rotation to occur, an eccentric force must be applied. In the human body, the contracting mus- cle applies an eccentric force (not to be confused with eccentric contraction) to the bone on which it attaches and causes the bone to rotate about an axis at the joint. The amount of torque can be determined by multiplying the force magnitude (amount of force) by the force arm. The perpen- dicular distance between the location of force application and the axis is known as the force arm, moment arm, or torque arm. The force arm may be best understood as the shortest distance
from the axis of rotation to the line of action of the force. The greater the distance of the force arm, the more torque produced by the force. A frequent practical application of torque and levers occurs when we purposely increase the force arm length in order to increase the torque so that we can more easily move a relatively large resistance. This is commonly referred to as increasing our leverage.
It is also important to note the resistance arm, which may be defined as the distance between the axis and the point of resistance application.
There is an inverse relationship between force and the force arm, just as there is between resistance and the resistance arm. The longer the force arm, the less force required to move the lever if the resistance and resistance arm remain constant, as shown graphically in Fig. 3.4. In addition, if the force and force arm remain con- stant, a greater resistance may be moved by short- ening the resistance arm. Because the muscular
force is applied internally, in musculoskeletal dis- cussions the force arm may also be referred to as the internal moment arm; and because the load is applied externally, the resistance arm may be referred to as the external moment arm.
Also, there is a proportional relationship between the force components and the resistance components. That is, for movement to occur when either of the resistance components increases, there must be an increase in one or both of the force components. Even slight variations in the location of the force and the resis- tance are important in determining the mechanical advantage (MA) and effective force of the muscle. This point can be illustrated with the simple for- mula shown in Fig. 3.8, using the biceps brachii muscle in each example.
The system of leverage in the human body is built for speed and range of motion at the expense of force. Short force arms and long resistance arms require great muscular strength to produce movement. In the forearm, the attachments of the biceps brachii and triceps brachii muscles clearly illustrate this point, since the force arm of the biceps brachii is 1 to 2 inches and that of the triceps brachii is less than 1 inch. Many similar examples are found all over the body. From a prac- tical point of view, this means that the muscular system should be strong to supply the necessary force for body movements, especially in strenuous sports activities.
When we speak of human leverage in relation to sport skills, we are generally referring to several levers. For example, throwing a ball involves levers at the shoulder, elbow, and wrist joints as well as from the ground up through the lower extremities and the trunk. In fact, it can be said that there is one long lever from the feet to the hand.
The longer the lever, the more effective it is in imparting velocity. A tennis player can hit a ten- nis ball harder (deliver more force to it) with a straight-arm drive than with a bent elbow, because the lever (including the racket) is longer and moves faster.
. In sports activities in which it is possible to increase the length of a lever with a racket or bat, the same principle applies.
In baseball, hockey, golf, field hockey, and other sports, long levers produce more linear force and thus better performance. However, to be able to fully execute the movement in as short a time as possible, it is sometimes desirable to have a short lever arm. For example, a baseball catcher attempt- ing to throw a runner out at second base does not have to throw the ball so that it travels as fast as when the pitcher is attempting to throw a strike. In the catcher’s case, it is more important to ini- tiate and complete the throw as soon as possible than to deliver as much velocity to the ball as pos- sible.
What’s the use o wheel and axle
Wheels and axles are used primarily to enhance range of motion and speed of movement in the musculoskeletal system. A wheel and an axle essentially function as a form of a first-class lever. When either the wheel or the axle turns, the other must turn as well. Both complete one turn at the same time. The centers of the wheel and the axle both correspond to the fulcrum. Both the radius of the wheel and the radius of the axle correspond to the force arms. If the radius of the wheel is greater than the radius of the axle, then the wheel has a mechanical advantage over the axle due to the longer force arm. That is, a relatively smaller force may be applied to the wheel to move a relatively greater resistance applied to the axle. Very simply, if the radius of the wheel is five times the radius of the axle, then the wheel has a 5 to 1 mechanical advantage over the axle, as shown in Fig. 3.10. The mechanical advantage of a wheel and an axle for this scenario may be calculated by considering the radius of the wheel over the radius of the axle application enables the wheel and axle to act as a second-class lever to gain force motion. Mechanical advantage = _ra_d_i_u_s\_\_o_f _t_h_e_w\_\_h_e_e_l divided by radius of the axle In this case the mechanical advantage is always more than 1.
If the application of force is reversed so that it is applied to the axle, then the mechanical advan- tage results from the wheel’s turning a greater dis- tance at greater speed. Using the same example, if the wheel radius is five times greater than the radius of the axle, the outside of the wheel will turn at a speed five times that of the axle. Addi- tionally, the distance the outside of the wheel turns will be five times that of the outside of the axle. This application enables the wheel and axle to act as a third-class lever to gain speed and range of motion. The mechanical advantage of a wheel and axle for this scenario may be calculated by considering the radius of the axle over the radius of the wheel. Mechanical advantage = _r_a_d_i_u_s_o_f\_\_th\_\_e_a_x_l_e_ divided radius of the wheel In this case the mechanical advantage is always less than 1.
An example of the muscles applying force to the axle to result in greater range of motion and speed may again be seen in the upper extrem- ity, in the case of the internal rotators attaching to the humerus. With the humerus acting as the axle and the hand and wrist located at the outside of the wheel (when the elbow is flexed approximately 90 degrees), the internal rotators apply force to the humerus. With the internal rotators concentrically internally rotating the humerus a relatively small amount, the hand and wrist travel a great distance. Using the wheel and axle in this manner enables us to significantly increase the speed at which we can throw objects.
Pulleys have a mechanical advantage of what?
Pulleys
Single pulleys have a fixed axle and function to change the effective direction of force applica- tion. Single pulleys have a mechanical advantage of 1, as shown in Fig. 3.11, A. Numerous weight machines utilize pulleys to alter the direction of the resistive force. Pulleys may be movable and can be combined to form compound pulleys to further increase the mechanical advantage. Every additional rope connected to movable pulleys increases the mechanical advantage by 1
In the human body, an excellent example is pro- vided by the lateral malleolus, acting as a pulley around which the tendon of the peroneus longus runs. As this muscle contracts, it pulls toward its belly, which is toward the knee. Due to its use of the lateral malleolus as a pulley (Fig. 3.12), the force is transmitted to the plantar aspect of the foot, resulting in downward and outward movement of the foot or eversion/plantar flexion
State and define the types of motion under the laws of motion and physical activities How is angular motion and linear motion related What is displacement Distance? Angular displacement Linear displacement Speed Velocity
• Displacement. If the path of movement is from A to B and then from B to C, the distance covered is AB + BC, but the displacement is the distance from A to C, or AC. If each cell is 1 square meter, then AB is 3 meters and BC is 3 meters, so the distance covered would be 6 meters. Using the Pythagorean Theorem (in a right triangle the square of the measure of the hypotenuse is equal to the sum of the squares of the measures of the legs, or a2 + b2 = c2), we can then determine the displacement (AC) to be 4.24 meters with AB2 + BC2 = AC2.
True or false
Newton’s laws explain all the characteristics of motion, and they are fundamental to understanding human movement.
True or false
activity. Body motion is generally produced, or at least started, by some action of the muscular system. Motion cannot occur without a force, and the muscular system is the source of force in the human body. Thus, development of the muscular system is indispensable to movement.
Basically, there are two types of motion: linear motion and angular motion. Linear motion, also referred to as translatory motion, is motion along a line. If the motion is along a straight line, it is recti- linear motion, whereas motion along a curved line is known as curvilinear motion. Angular motion, also known as rotary motion, involves rotation around an axis.
the axis of rota- tion is provided by the various joints. In a sense, these two types of motion are related, since angular motion of the joints can produce the linear motion of walking. In many sports activities, the cumula- tive angular motion of the joints of the body imparts linear motion to a thrown object (ball, shot) or to an object struck with an instrument (bat, racket).
Displacement is a change in the position or loca- tion of an object from its original point of refer- ence, whereas distance, or the path of movement, is the actual sum length it is measured to have trav- eled. Thus an object may have traveled a distance of 10 meters along a linear path in two or more directions but be displaced from its original refer- ence point by only 6 meters. Fig. 3.14 provides an example. Angular displacement is the change in location of a rotating body. Linear displacement is the distance a system moves in a straight line.
Speed is how fast an object is moving, or the distance an object travels in a specific amount of time. Velocity, the rate at which an object changes its position, includes the direction and describes the rate of displacement.
State the law of inertia
What is inertia
State some examples of inertia
Law of inertia
A body in motion tends to remain in motion at the same speed in a straight line unless acted on by a force; a body at rest tends to remain at rest unless acted on by a force.
Inertia can be described as the resistance to action or change. In terms of human movement, inertia refers to resistance to acceleration or decel- eration. Inertia is the tendency for the current state of motion to be maintained, whether the body segment is moving at a particular velocity or is motionless.
Muscles produce the force necessary to start motion, stop motion, accelerate motion, deceler- ate motion, or change the direction of motion. Put another way, inertia is the reluctance to change sta- tus; only force can do so. The greater the mass of an object, the greater its inertia. Therefore, the greater the mass, the more force needed to significantly change an object’s inertia
ties. A sprinter in the starting blocks must apply considerable force to overcome resting inertia. A runner on an indoor track must apply considerable force to overcome moving inertia and stop before hitting the wall.
Because force is required to change inertia, it is obvious that any activity that is carried out at a steady pace in a consistent direction will conserve energy and that any irregularly paced or directed activity will be very costly to energy reserves. This explains in part why activities such as handball and basketball are so much more fatiguing than jogging and dancing
What is the law of acceleration under laws of motion
What is acceleration
What is mass
Law of acceleration
A change in the acceleration of a body occurs in the same direction as the force that caused it. The change in acceleration is directly proportional to the force causing it and inversely proportional to the mass of the body.
Acceleration may be defined as the rate of change in velocity. To attain speed in moving the body, a strong muscular force is generally neces- sary. Mass, the amount of matter in a body, affects the speed and acceleration in physical movements. A much greater force is required from the muscles to accelerate an 80-kilogram man than to acceler- ate a 58-kilogram man to the same running speed. Also, it is possible to accelerate a baseball faster than a shot because of the difference in mass. The force required to run at half speed is less than the force required to run at top speed. To impart speed to a ball or an object, it is necessary to rapidly accel- erate the part of the body holding the object.
What is the law of reaction
Law of reaction
For every action there is an opposite and equal reaction.
As we place force on a supporting surface by walking over it, the surface provides an equal resis- tance back in the opposite direction to the soles
of our feet. Our feet push down and back, while the surface pushes up and forward. The force of the surface reacting to the force we place on it is referred to as ground reaction force. We provide the action force, while the surface provides the reaction force. It is easier to run on a hard track than on a sandy beach because of the difference in the ground reaction forces of the two surfaces. The track resists the runner’s propulsion force, and the reaction drives the runner ahead. The sand dis- sipates the runner’s force, and the reaction force is correspondingly reduced, with an apparent loss in forward force and speed (Fig. 3.16). A sprinter applies a force in excess of 1335 Newtons on the starting blocks, which resist with an equal force. When a body is in flight, as in jumping, move- ment of one part of the body produces a reaction in another part because there is no resistive surface to supply a reaction force.
What is friction
Friction is of two types
Name them and define them
G. 3.17 • Friction. A, Static friction; B, Static friction also, but less than in A because there is less mass (weight); C, Kinetic friction is always less than static friction; D, Rolling friction is always less than kinetic friction
True or false
How can static friction be increased
How can you deteRmine the amount of friction forces ?
What is the coefficient of friction
What is rolling friction
Friction is the force that results from the resis- tance between the surfaces of two objects moving on each other. Depending on the activity involved, we may desire increased or decreased friction. In running, we depend on friction forces between our feet and the ground so that we may exert force against the ground and propel ourselves forward. When friction is reduced due to a slick ground or shoe surface, we are more likely to slip. In skating, we desire decreased friction so that we may slide across the ice with less resistance
Friction may be further characterized as either static or kinetic. Static friction is the amount of friction between two objects that have not yet begun to move, whereas kinetic friction is the fric- tion between two objects that are sliding along each other. Static friction is always greater than kinetic friction. As a result, it is always more dif- ficult to initiate dragging an object across a surface than it is to continue dragging it. Static friction may be increased by increasing the normal or perpen- dicular forces pressing the two objects together, as by adding more weight to one object sitting on another object.
To determine the amount of fric- tion forces, we must consider both the forces press- ing the two objects together and the coefficient of friction, which depends on the hardness and roughness of the surface textures. The coefficient of friction is the ratio of the force needed to over- come the friction to the force holding the surfaces together. Rolling friction is the resis- tance to an object rolling across a surface, such as a ball rolling across a court or a tire rolling across the ground. Rolling friction is always much less than static or kinetic friction.
