Work and Power.

Work vs. Impulse Similarities: both have a force component exerted on an object; both answer the question “how long” a force acts. Differences: work describes “how long” a force acts in terms of distance; Impulse describes “how long” a force acts in terms of time. Work = Force * distance W = F*d Impulse = Force * time I = F*t

Work Transfer of energy through motion Depends on the amount of force and distance The product of the component of the force exerted on an object in the direction of the displacement (change in position). Defined as force times distance. W = F*d, where w –work, units J (joules) or N*m F – force, units N (Newtons) D – distance, units m (meters)

Examples of Work Lifting textbooks two things happen: 1. A force is exerted on the textbook. 2. The textbook is moved by that force. If the textbook is simply held still, I will get tired and feel like I am doing work. My heart is contracting which produces the force and moves blood a distance throughout my body. However, I am doing no work on the textbook unless I exert a force to move the book. If I push on the wall am I doing work? No, I am not moving the wall, but I am exerting a force.

Power

Question If a forklift is replaced with a new forklift that has twice the power, how much greater a load can it lift in the same amount of time? If it lifts the same load, how much faster can it operate? Twice the amount of power will lift twice the load in the same time or the same load in half time.

Formula Organizer FormulaVariablesUnits Work: W = F*d W – work, F – force, d - distanceJoule (J) or N*m P – power, W – work, t- time Weight: w = m*g (lowercase) w- weight, m – mass, g – gravitational acceleration