Biomechanical Systems and Static Equilibrium

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Questions and Answers

What are the two essential elements of work?

Energy and momentum

Force and displacement (correct)

Mass and velocity

Force and acceleration

What is the unit of work in SI units?

Watt.Second

Newton.Meter (correct)

Joule.Meter

Kilogram.Meter

What happens to the work done if the distance is zero?

The work is infinite

The work is zero (correct)

The work is maximum

The work is minimum

What is the direction of the force that does work on an object?

Parallel to the direction of motion Signup and view all the answers

What is the nature of work in physics?

A scalar quantity Signup and view all the answers

What is the equation for work done?

W = Fs Signup and view all the answers

What is the relationship between force and displacement in work?

Force and displacement do not point in the same direction Signup and view all the answers

What is the component of force that does work on an object?

Component of force parallel to displacement Signup and view all the answers

What is the condition for maximum work to be done?

Force and displacement are parallel Signup and view all the answers

What is the work done when the force is at right angles to the displacement?

0 J Signup and view all the answers

What is the unit of energy in SI units?

Joule Signup and view all the answers

What is the relationship between work and energy?

There is a one-to-one correspondence between work and energy Signup and view all the answers

What is the component of force that does work?

The component parallel to the displacement Signup and view all the answers

What is energy?

The ability to do work Signup and view all the answers

What is the condition for negative work to be done?

Force and displacement are opposite Signup and view all the answers

What is conserved in all physical processes?

Energy Signup and view all the answers

What is the work done on an object by a force F directed at an angle θ relative to the displacement?

(Fcosθ)s Signup and view all the answers

When is the force component perpendicular to the displacement?

When θ = 90 Signup and view all the answers

What is the sign of the work done when the component of the force points in the opposite direction to the displacement?

Negative Signup and view all the answers

A force F is applied to an object at an angle θ to the displacement. What is the work done if θ = 90?

0 Signup and view all the answers

What is the units of work done?

Joules (J) Signup and view all the answers

A weight lifter lifts a barbell with a weight of 710 N a distance of 0.65 m above his chest. What is the work done by the weight lifter during the lifting phase?

460 J Signup and view all the answers

What is the work done during the lowering phase of the weight lifter's motion?

-460 J Signup and view all the answers

A box is pushed with a force of 40 N and moves steadily through a distance of 3 m in the direction of the force. What is the work done?

120 J Signup and view all the answers

Study Notes

Static Equilibrium

A body is in static equilibrium if both its linear and angular acceleration are zero.
The sum of the force acting on the body, as well as the sum of torques produced by these forces, must be zero.

The Work

In Physics, work is done only if an object is moved through some displacement while a force is applied to it.
Force and displacement are two essential elements of work.
Only the force parallel to the direction of motion does work on the object.
Work (W) is defined as the magnitude F of the force times the magnitude s of the displacement: W = Fs.
The unit of work is Newton.Meter (N.m) in SI unit, which is also referred to as a joule (J).
Work is a scalar quantity and does not convey directional information.
If the distance s is zero, the work is zero, even if a force is applied.
The idea of work is intimately tied up with the idea of motion.

Force and Displacement at an Angle

If the force and displacement do not point in the same direction, only the component of the force along the displacement is used to define the achieved work: W = (Fcosθ)s.
When the force points in the same direction as the displacement, θ = 0 and W = Fs.
The force component perpendicular to the displacement does not work.
If the entire force is perpendicular to the displacement, the angle θ is 90°, and the force doesn't work at all.

Positive and Negative Work

Work can be either positive or negative, depending on whether the component of the force points in the same direction as the displacement or in the opposite direction.
Example: bench press, where the weight lifter raises the barbell a distance of 0.65 m above his chest, resulting in positive work during the lifting phase and negative work during the lowering phase.

Examples of Work

Example 1: Lifting a barbell with a weight of 710 N, the work done by the weight lifter is 460 J during the lifting phase and -460 J during the lowering phase.
Example 2: A box is pushed with a force of 40 N and moves steadily through a distance of 3 m in the direction of the force, resulting in a work done of 120 J.
Example 3: A 600 N force is applied to a dresser that moves 2 m, resulting in different work done depending on the direction of the force and displacement.

Energy

In Physics, energy is defined as the ability to do work.
Energy is an important concept, it is a scalar quantity with SI units of joules (J).
Energy is a derived unit equivalent to newton meters (N m).
Energy is associated with widely different phenomena, such as Atomic Energy, Heat energy, Potential Energy, Solar Energy, Kinetic Energy, etc.
The concept of work is similar to that of energy, but we usually associate energy with a body and work with a force.
In all physical processes, energy is conserved.
There is one-to-one correspondence between work and energy, it takes 2J of energy to do 2J of work.