BIOMECHANICS WORK Work done by the force is

BIOMECHANICS

WORK Work done by the force is defined to be the product of component of force in the direction of the displacement and the magnitude of this displacement. W=F. d (force x displacement) *if there is no displacement there is no workdone. Eg; when you push hard against a rigid brick wall, the force you excert on the wall does not work. yet the muscles are alternatively contracting and relaxing and internal energy is being used up and you get tired. *unit of work is joule (j).

TORQUE(MOMENT OF FORCE) • • • The rotational analogue of force is torque. It is also called as couple. T=rx F (r=position vector) In order to find a linear force we need to know a mass and an acceleration. However, torque is a little different, thanks to rotation being involved. Think about opening a door. Where do you push on it when you want it to open? You push on the side of the door where there are no hinges because pushing on the side with the hinges would make it much harder to open. So for torque, we need to know not only the mass and acceleration of a linear force, but also how far that force is from the axis of rotation, since we can get different results depending on that, as well. We can see this in the diagram and equation for torque. r has units of meters (m), and F has units of Newtons (N). Combining these together, we see that a unit of torque is a Newton-meter (Nm).

FRICTION • Frictional force opposes relative motion between two surface in contact. • Eg; body of mass ‘m’ is at rest on horizontal table , where force F is applied. • Eg; *Rubbing both hands together to create heat. *The friction between two books when sliding one into place on a bookshelf. The friction between the bottom of a book and the shelf when being slid into place.

ACCELERATION • Rate of change of velocity with distance. • Rate of change of velocity with time is a constant of motion for all object in free fall , on other hand the change in velocity with distance is not constant , it decreases with increasing distance of fall. • The average acceleration ‘a’ over a time interval is define as the change of velocity divided time interval. a=Δv/Δt

POWER • Power is defined as energy per sec. • Power is rate of doing work. • Unit of power is ’watt’

FORCE • A force is a push or pull upon an object resulting from the object's interaction with another object. Whenever there is an interaction between two objects, there is a force upon each of the objects. When the interaction ceases, the two objects no longer experience the force. Forces only exist as a result of an interaction. • Units of Measurement/Force SI unit of Force is Newtons (N). 1 Newton is equal to 1 kg* m*s^-2. The basic formula force is F=ma where F stands force, m stands for mass in kilograms and a stands for acceleration in m*s^-2.

NEWTONS LAW • First law: If the net external force on a body is zero , its acceleration is zero. Acceleration can nonzero only if there is a net external force on the body. eg: ★A spaceship out in interstellar space , far from all other object and with all its rockets turned off , has no net external force acting on it. Its acceleration according to first law must be zero , if it is in motion it must continue in uniform velocity. ★ A book at rest on the table and a car moving with uniform velocity.

• Second law: The rate of change of momentum of a body is directly proportional to the applied force and takes place in the direction in which the force act. eg: ★ A seasoned cricketer draws in his hand during a catch , allowing greater time for the ball to stop and hence require a smaller force. ★Rotating a stone in a horizontal circle with uniform speed by means of a string.

• Third law: To every action there is always an equal and opposite reaction. Eg : ★ Bullet coming out of the gun. ★Pressing a coiled spring.

GRAVITY • The force of attraction between all masses in the universe , especially the attraction of the earth mass for bodies near its surface.

CENTER OF GRAVITY • The center of gravity (CG) of an object is the point at which weight is evenly dispersed and all sides are in balance. A human's center of gravity can change as he takes on different positions, but in many other objects, it's a fixed location.

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