SfC Home > Physics > Gravity and Gravitation >

 

Key words: work, gravity, inertia, air resistance, drag, acceleration, velocity, physics, physical science, Ron Kurtus, School for Champions. Copyright © Restrictions

Work Against Gravity to Lift an Object

by Ron Kurtus (revised 27 June 2013)

When an object is lifted or projected upward, work must be done against the resistance from gravity. In some situations, the resistance of inertia from accelerating the object and air resistance must be taken into account.

If the object is already moving upward at some initial velocity, the work done by gravity is simply the force of gravity times the displacement, provided the velocity is constant and small enough that air resistance is neg liable.

If the object is accelerated during the lifting process, the resistance from inertia must be taken into account. If the object is projected upward at a high velocity, air resistance must be added to the equation.

Questions you may have include:

This lesson will answer those questions.



Useful tool: Metric-English Conversion

Already moving upward

If an object has an initial upward velocity and some force is continuing to move it upward at that constant velocity, the force required to move the object equals the restive force of gravity:

FT = Fg

Fg = mg

where

The work required to lift the object is:

W = mgy

where

Accelerating upward

If an object is stationary or moving upward at some initial velocity, a sufficient upward force can accelerate the object to higher velocities, The upward force must be greater than the downward force of gravity in order to accelerate the object upward.

Most often the air resistance in relatively low upward acceleration is negligible.

The upward force is:

FT = Fi + F

FT = ma + mg

where

Th resulting work required to lift and accelerate an object is:

W = m(a + g)y

If the object is accelerated to some height and then is continued to be lifted at a constant velocity, the work becomes:

W = m(a + g)y1 + mgy2

High velocity acceleration

When an object, such as a rocket, is acceleration upwards at a high velocity, air resistance becomes an added factor in the work required.

The total upward force to propel a rocket upward is:

FT = Fg + Fi + Fa

FT = mg + ma + kv2

where

The work required to propel a rocket to some altitude is:

WT = FTy

WT = (mg + ma + kv2)y

Summary

When an object is lifted or projected upward, work must be done against the resistance from gravity, inertia and air resistance.

If the object is moving upward at constant velocity, the work done by gravity is simply the force of gravity times the displacement. If the object is accelerated during the lifting process, the resistance from inertia must be taken into account. If the object is projected upward at a high velocity, air resistance must be added to the equation.


Hard work will get you far in life


Resources and references

Ron Kurtus' Credentials

Websites

Work by gravity by Sunil Kumar Singh - Connexions

Gravity and Inertia in Running - Locomotion and Biology paper (PDF)

Gravity Resources

Books

Top-rated books on Simple Gravity Science

Top-rated books on Advanced Gravity Physics


Questions and comments

Do you have any questions, comments, or opinions on this subject? If so, send an email with your feedback. I will try to get back to you as soon as possible.


Share

Click on a button to bookmark or share this page through Twitter, Facebook, email, or other services:

 

Students and researchers

The Web address of this page is:
www.school-for-champions.com/science/gravity_work_against_gravity.htm

Please include it as a link on your website or as a reference in your report, document, or thesis.


Where are you now?

School for Champions

Gravity and Gravitation topics

Work Against Gravity to Lift an Object



Gravity and Gravitation

Gravity topics

Basics

Derivations of equations

Falling objects

Projected downward

Projected upward

Gravity and energy

Gravity and work

Gravity applications

Gravitation



Let's make the world a better place

Be the best that you can be.

Use your knowledge and skills to help others succeed.

Don't be wasteful; protect our environment.

You CAN influence the world.





Live Your Life as a Champion:

Take care of your health

Seek knowledge and gain skills

Do excellent work

Be valuable to others

Have utmost character

Be a Champion!



The School for Champions helps you become the type of person who can be called a Champion.