Hey there Sign in to join this conversationNew here? Join for free

Calculating a value for g by a free fall method.

Announcements Posted on
Study Help needs new mods! 14-04-2014
Post on TSR and win a prize! Find out more... 10-04-2014
    • Thread Starter
    • 0 followers
    Offline

    ReputationRep:
    Can someone please tell me a method, I'm very confused as I still have chemistry whirling around in my head :mad: thanx
    • 0 followers
    Offline

    ReputationRep:
    Objective

    To measure the acceleration due to gravity by a free fall method.

    Theory

    An object falling freely under gravity, assuming that air resistance effects can be neglected, obeys the following equation:

    s = ut + ½at²(1)

    Apparatus

    A ball bearing is held vertically above a mechanical plate by means of a small electromagnet. When the current through the magnet is switched off, the ball bearing falls from rest until it hits the plate. An electric stop-clock records the time of fall, since the start signal to the clock is synchronised with the release of the ball-bearing and the stop signal with the closing of a switch actuated by the plate.

    Experimental Procedure

    1. For a particular value of s, record the fall time t. Take several readings of t for each value of s in order to estimate the error in measuring t.
    2. Measure the fall times for 8 values of s. Try to cover as large a range of distances as possible. Consider carefully the value of s (Is there a systematic error possible here?)

    Method of Analysis

    1. Present your results graphically by plotting against s. From the error D[delta]t on t, evaluate the error 2t[delta]t on and draw this on each plotted point.
    2. Since the ball bearing falls from rest, u = 0. Hence s=½at² or t²=(2/a)s. The gradient of the graph (with s being plotted along the horizontal axis) is therefore 2/a.
    3. Find the gradient and the error in the gradient from your graph.
    4. Calculate g and the error in g.
    • Thread Starter
    • 0 followers
    Offline

    ReputationRep:
    (Original post by OldakQuill)
    Objective

    To measure the acceleration due to gravity by a free fall method.

    Theory

    An object falling freely under gravity, assuming that air resistance effects can be neglected, obeys the following equation:

    s = ut + ½at²(1)

    Apparatus

    A ball bearing is held vertically above a mechanical plate by means of a small electromagnet. When the current through the magnet is switched off, the ball bearing falls from rest until it hits the plate. An electric stop-clock records the time of fall, since the start signal to the clock is synchronised with the release of the ball-bearing and the stop signal with the closing of a switch actuated by the plate.

    Experimental Procedure

    1. For a particular value of s, record the fall time t. Take several readings of t for each value of s in order to estimate the error in measuring t.
    2. Measure the fall times for 8 values of s. Try to cover as large a range of distances as possible. Consider carefully the value of s (Is there a systematic error possible here?)

    Method of Analysis

    1. Present your results graphically by plotting against s. From the error D[delta]t on t, evaluate the error 2t[delta]t on and draw this on each plotted point.
    2. Since the ball bearing falls from rest, u = 0. Hence s=½at² or t²=(2/a)s. The gradient of the graph (with s being plotted along the horizontal axis) is therefore 2/a.
    3. Find the gradient and the error in the gradient from your graph.
    4. Calculate g and the error in g.
    Thanx very much! Appreciated I've just had a thought can I also use the pendulum method? I.e using T= 2pi root l/g ? and do it that way
    • 0 followers
    Offline

    ReputationRep:
    well u can use that, or : that's the method used.
    but ur question is : how to find g using FREE FALL
    • 0 followers
    Offline

    ReputationRep:
    Thanks, that was really useful , one small question though, how do you calculate g at the end?
    • 45 followers
    Offline

    ReputationRep:
    (Original post by emfish)
    Thanks, that was really useful , one small question though, how do you calculate g at the end?
    gradient is 2/a where a is the accelration due to gravity ie g. hence g= 2/ gradient
Updated: June 11, 2005
Article updates
Reputation gems:
You get these gems as you gain rep from other members for making good contributions and giving helpful advice.