Free fall Definition and 486 Threads

In Newtonian physics, free fall is any motion of a body where gravity is the only force acting upon it. In the context of general relativity, where gravitation is reduced to a space-time curvature, a body in free fall has no force acting on it.
An object in the technical sense of the term "free fall" may not necessarily be falling down in the usual sense of the term. An object moving upwards might not normally be considered to be falling, but if it is subject to only the force of gravity, it is said to be in free fall. The Moon is thus in free fall around the Earth, though its orbital speed keeps it in very far orbit from the Earth's surface.
In a roughly uniform gravitational field, in the absence of any other forces, gravitation acts on each part of the body roughly equally. When there is no normal force exerted between a body (e.g. an astronaut in orbit) and its surrounding objects, it will result in the sensation of weightlessness, a condition that also occurs when the gravitational field is weak (such as when far away from any source of gravity).
The term "free fall" is often used more loosely than in the strict sense defined above. Thus, falling through an atmosphere without a deployed parachute, or lifting device, is also often referred to as free fall. The aerodynamic drag forces in such situations prevent them from producing full weightlessness, and thus a skydiver's "free fall" after reaching terminal velocity produces the sensation of the body's weight being supported on a cushion of air.

View More On Wikipedia.org
  1. J

    What is the speed of a falling rock at t = 6 sec?

    The equation for free fall at the surface of the planet Quixon is s = 3.8t2m with t in sec. Assume a rock is dropped from the top of a 400-m cliff. Find the speed of the rock at t = 6 sec. The problem is.. i don't know if the "m" is part of the equation or not.. like should i plug in the 400 as...
  2. K

    Calculate Distance of Roof Above Window Top

    A roof tile falls from rest from the top of building. An observer inside the building notices that it takes 0.20 s for the tile to pass her window, whose height is 1.6 m. How far above the top of this window is the roof? I attempted this question about 2 or 3 different ways but they don't...
  3. K

    Calculating the Magnitude of an Object in Free Fall

    Heres the question: an 32.8 Newton object is in free fall.what is the mangniutude of the object if it encounters air resistance of 16.6 Newtons? I think you subtract cause air resistance cuts down force: 32.8 - 16.6 = 16.2 Newtons So am i right or do i need to use another equation?
  4. K

    How Does Free Fall Affect Pepe and Babette's Midair Catch?

    Pepe, the clown, is jumping on a trampoline as Babette, the tightrope walker, above him suddenly loses her balance and falls off the tightrope straight toward Pepe. Pepe has just started upward at 15.0 m/s when Babette begins to fall. Pepe catches her in midair after 10.0s. a) How far has...
  5. D

    Physics Motion and Free Fall Equations

    I am just looking for--or perhaps one of u could just post them--a list of physics motion equations in 1d, and freefall u know v=x/t v(f)=v(i)... v(f)2=v(i)2...etc thx
  6. E

    How Does Air Resistance Affect the Distance of Free Fall?

    Here's the problem: Consider a particle of mass m whose motion starts from rest in a constant gravitational field. If a resisting force proportional to the square of the velocity (kmv2) is encountered, find the distance s the particle falls in accelerating from v0 to v1. I began with the...
  7. K

    Calculating Velocity in Free Fall from a Given Height

    ok how would i go about solving this an what equations do i use [SFHS99 2.P.40.] A worker drops a wrench from the top of a tower 89.0 m tall. With what velocity does the wrench strike the ground? (Assume the positive direction is upward.) wrong check mark m/s i have to use this...
  8. L

    Force and Free Fall: 3 Questions Answered

    Can anyone help me with any of these 3 questions? 1. Wrongly called for a foul, any angry basketball player throws the ball straight down to the floor. If the ball bounces straight up and returns to the floor 2.5s after first striking it, what was the ball's greatst height above the floor...
  9. R

    Max Height of Rocket in Free Fall: Solving for a, t1, and g

    I was given the situation, A rocket, initially at rest on the ground, accelerates straight upward from rest with constant net acceleration a , until time t1, when the fuel is exhausted. Find the maximum height H that the rocket reaches (neglecting air resistance). Express the maximum height...
  10. U

    What Does the Constant 'b' Represent in the Drag Force Equation?

    free fall with drag force If the equation F=-bv^2 describes the drag force of an object...then the differential equation for the object's motion would be: dv/dt= -g+bv/m or is it... dv/dt= g-bv/m After solving the equation, should I get... V=mg/b[1-e^(-bt/m)] Also, does this...
  11. B

    How Long Does a Cricket Take to Jump Portions of Its Full Leap?

    Heres the question: Some crickets can jump 21 cm, how long does it take the cricket to jump 7cm of that 21cm?
  12. kat

    News Stock on Kerry in an IEM free fall

    Stock on Kerry in an IEM "free fall" Market Quotes: Pres04_WTA.html Quotes current as of 12:31:43 CST, Monday, September 27, 2004. Symbol Bid Ask Last Low High Average DEM04_G52 0.061 0.069 0.067 0.067 0.077 0.072 DEM04_L52 0.210 0.219 0.225 0.207 0.232 0.226 REP04_L52 0.230 0.231...
  13. F

    Free fall (check my solution im stuck) PLEASE HELP ME TODAY

    Q40. A boy stands at the edge of a bridge 20.0 m above a river and throws a stone straight down with a speed of 12.0 m/s. He throws another pebble straight upward with the same speed so that it misses the edge of the bridge on the way back down and falls into the river. For each stone find (a)...
  14. F

    How Long Does It Take for a Dart to Reach the Board from 1.9m?

    ''A DART LEAVES THE THROWER HAND HORIZONTALLY AT A height of 1.9m above the ground, calculate the time taken by the dart to reach the board and the horizontal velocity at which the dart left the throwers hand.'' this is what iv worked out x-0.4 u-? v-0 a-0 t-? i than went onto finding...
  15. B

    Solving for Raft Speed in a Free Fall Problem | Bridge, Stone, and River Math

    This class is killing me. Here's my problem: A woman on a bridge 91.0m high sees a raft floating at a constant speed on the river below. She drops a stone from rest in an attempt to hit the raft. The stone is released when the raft has 2.70m more to travel before passing under the bridge. The...
  16. B

    Vector and Free Fall Problem Solving

    Hi again, My first question has to do with vectors again. But it's not hard. I just can't see my mistake. The problem involves two displacement vectors. A which is 3.00km due south, and B which points due east. No value is given for B. However the resultant vector is 4.49km. So of...
  17. C

    Free fall acceleration flowerpot problem

    A flowerpot falls off a windowsill and falls past the window below. You may ignore air resistance. It takes time 0.420 s to pass this window, which is of height 1.90 m. Question- How far is the top of the window below the windowsill from which the flowerpot fell? Take the free fall...
  18. C

    Free Fall Question: Calculate Velocity & Distance

    A student throws a water balloon vertically downward from the top of a building. The balloon leaves the thrower's hand with a speed of 6.35m/s . Air resistance may be ignored, so the water balloon is in free fall after it leaves the thrower's hand. A.) What is its speed after falling for a...
  19. S

    Free Fall Problem: Calculating Projectile Motion from a Cliff Edge

    Help! Free Fall Problem A pellet gun is fired straight downward from the edge of a cliff that is 13 m above the ground. The pellet strikes the ground with a speed of 30 m/s. How far above the cliff edge would the pellet have gone had the pellet been fired straight upward?
  20. C

    Hot Air Balloon Free Fall Question

    A hot-air balloonist, rising vertically with a constant velocity of magnitude v=5.00m/s , releases a sandbag at an instant when the balloon is a height h=40.0m above the ground . After it is released, the sandbag is in free fall. 1.) Compute the position of the sandbag at a time 0.165s after...
  21. E

    Rocket Free Fall Problem: Calculating Time, Altitude, and Velocity

    Pleeeeeeeeeeeeeeeeease Help! A test rocket is fired vertically upward from a well. Acatapult gives it an initial speed of 79.2 m/s at ground level. Its engines then fire and it accelerates upward at 4.10 m/s^2 until it reaches an altitude of 950m. At that point its engines fail, and the...
  22. W

    Calculating Basketball Player's Hang Time

    A basketball player jumps 1 meter high off the ground, turns around and starts back down. Estimate the time she is within 30 cm of the top of her trajectory (her hang time.) (HINT: Calculate the time it takes to fall 30 cm from rest and double it.) Explain why that works note...
  23. E

    Initial Speed of Ball Thrown Horizontally from 15.75m Height

    A ball is thrown horizontally from a height of 15.75 m and hits the ground with a speed that is 5.0 times its initial speed. What was the initial speed? I thought you might have to find time and I got t=1.79s, but after that I cannot seem find my way to the answer Thanks to whom ever can...
  24. P

    How can I solve this free fall problem with missing variables?

    Stumped on free fall problem! This is probably an easy question, but I am stumped!A wrecking ball is hanging at rest from a crane when suddenly the cable breaks. The time it takes for the ball to fall halfway to the ground is 1.2s. Find the time it takes for the ball to fall from rest all the...
  25. S

    Find Velocity for Object to Reach Space & Return in 8 Days

    I am trying to find a velocity for an object that would launch it into space from Earth (straight up, NOT into orbit) and return exactly 8 days later. I cannot use x = v0t + 1/2at^2 (x=0 t=691200 a=9.8 [seconds in 8 days]) because the distance from the Earth changes in such a great way that...
  26. C

    Solve Physics Free Fall Question: Height of Building

    I'm really bad at physics so please excuse me. But I would like some help on this question. I would like to be able to solve it without plugging in any numbers until the end. If a person steps off a building of height h, and free falls on the way down to the bottom. What is the height of the...
  27. H

    The difference b/t free fall and outer space

    You are in the closed elevator with the apple. You feel weightless. So you want to know whether you're free falling or in the outer space. Place the apple about a meter away from your eyes. If the elevator is in free fall, the apple will move close to you slowly, but if you're in the outer...
  28. holly

    Free Fall Problems: Solving for Speed Without Calculus - Formula Included

    I have read through the other free fall problems here on the boards and still cannot correctly solve the following: One-half second after starting from rest, a freely falling object will have a speed of about: a)10 m/s b)2.5 m/s c)5 m/s d)20 m/s I find the answer to be (b), 2.5 m/s, but...
  29. P

    Does the elevator speed going up effect the free fall time?

    I ran across this physics problem in class yesterday, it seems simple but...... (assume simplest case) ok...a screw at the top of an elevator that is traveling upwards comes loose and falls. Does the elevator speed going up effect the free fall time? (like does the elevator move toward the...
  30. P

    What Is the Correct Expression for Velocity in Free Fall with Air Resistance?

    An object is releaseed from rest at time t = 0 and falls through the air, which exerts a resistive force such that the acceleration a of the object is given by a = g - bv, where v is the object's speed and b is a constant. If limiting cases for large and small values of t are considered, which...
  31. P

    Discover Free Fall Equations & Solve for Time and Height | g = 9.8 m/s

    Can anyone help me out with some free fall equations? and: Assume: g = 9.8 m/s A stone falls from rest from the top of a cliff. A second stone is thrown downward from the same height 2.1 seconds later with an initial speed of 41.16 m/s. They hit the ground at the same time. How long...
  32. M

    Stone dropping - yet another free fall acceleration problem

    I'm sorry, I am just having difficulty with being sure of myself when it comes to these problems. This one states: A stone is dropped into a river from a bridge 43.9m above the water. Another stone is thrown vertically down 1.00 s after the first is dropped. Both stones strike the water at...
  33. M

    Model rocket - free fall acceleration again

    model rocket - free fall acceleration again :( The problem states: A model rocket fired vertically from the ground ascends with a constant vertical acceleration of 4.0 m/s^2 for 6.00 seconds. Its fuel is then exhausted, so it continues upward as a free-fall particle and then falls back down...
  34. agro

    Find the Angle for Maximum x Position in Free Fall Motion

    Consider a particle located at (x0, y0), having inital velocity v0, and the angle of inclination of the velocity vector is [the]. The particle is subjected to a vertical acceleration of -g. It's equation of motion is... x = x0 + v0*cos[the]*t y = y0 + v0*sin[the]*t - 0.5*g*t2 If t>0...
  35. M

    Free fall of ball and acceleration

    I suppose I am having trouble with this problem because there are no numbers given. Here is the problem: A ball is thrown down vertically with an initial speed of Vo from a height of h. a) What is its speed just before it strikes the ground? Speed is just the magnitude of instantaneous...
  36. D

    The G force is not infinity at distance zero(in free fall)

    i'm talking about droping a ball into a free fall under assumption that it can pass thru the Earth's center all the way to minus height point. case 1:if you say that the force at the dropping point is F=G(/m/R)(M/R)<>0 then the equilibrium point is the center of the earth.but when the ball...
Back
Top