Force & Work: Understanding the Calculus Behind it All

AI Thread Summary
Pounds are treated as a unit of force rather than mass because they represent weight, which is the gravitational force acting on an object. The slug is the corresponding unit of mass in the English system. Although the pound has been defined as a unit of mass, it is commonly used to denote force in practical applications. The term "pound-weight" clarifies this distinction, particularly when referring to gravitational force. Understanding this differentiation is crucial for accurately applying concepts of force and work in calculus.
opticaltempest
Messages
135
Reaction score
0
I am reading over an explanation of Work in my calculus textbook (Early Trancendentals 5e - Stewart). The following example has me confused. Why are pounds treated as a force and not a mass?

http://img71.imageshack.us/img71/8987/forceandwork6ok.jpg
 
Last edited by a moderator:
Physics news on Phys.org
because lbs are a unit of force. the slug is the unit of mass for the english system
 
The pound has actually been officially defined as a unit of mass, even though I believe it was used as a unit of force a long time ago. Nowadays the term pound-weight is used to refer to the gravitational force exerted by a pound, and if you notice the main question states "20-lb weight" to specify this, even though it neglects to be so specific in the rest of the text.
 
Thread 'Variable mass system : water sprayed into a moving container'

Thread 'Variable mass system : water sprayed into a moving container'

Starting with the mass considerations #m(t)# is mass of water #M_{c}# mass of container and #M(t)# mass of total system $$M(t) = M_{C} + m(t)$$ $$\Rightarrow \frac{dM(t)}{dt} = \frac{dm(t)}{dt}$$ $$P_i = Mv + u \, dm$$ $$P_f = (M + dm)(v + dv)$$ $$\Delta P = M \, dv + (v - u) \, dm$$ $$F = \frac{dP}{dt} = M \frac{dv}{dt} + (v - u) \frac{dm}{dt}$$ $$F = u \frac{dm}{dt} = \rho A u^2$$ from conservation of momentum , the cannon recoils with the same force which it applies. $$\quad \frac{dm}{dt}...
View full post »

Similar threads

Find work given two conservative forces and a nonconservative force
Replies
9
Views
833
Having a hard time learning Newton's 2nd law
Replies
5
Views
2K
Understanding work in translation and rotation of a magnetic dipole
Replies
1
Views
2K
Work Done By a Spring's Restoring Force
Replies
4
Views
1K
Understanding the Forces Behind Part B of the Graph
Replies
10
Views
2K
James Stewart Calculus replacement
Replies
12
Views
4K
Kumon Math and Similar Programs
Replies
6
Views
3K
Work to stretch a spring question (nvm, figured it out)
Replies
5
Views
1K
Inverse square law of gravitation and force between two spheres
Replies
8
Views
2K
How does an eddy current brake work exactly?
Replies
2
Views
2K

Hot Threads

Recent Insights

Back
Top