# Simple lab with two blocks and pulley

• fisselt
In summary, the conversation discusses the results of three tests using two blocks on a horizontal plane with a string and pulley system. The tests show a significant difference between the predicted and actual accelerations, with the addition of weight on one block causing even more discrepancy. The conversation also mentions the use of an equation to predict acceleration and the potential role of friction in the results. Further calculations show a loss of acceleration and the possibility of a 10% reduction per 0.1kg added weight, but this still does not account for all the lost acceleration. The speaker is seeking help to understand the discrepancies and determine the correct equation for calculating acceleration in this scenario.
fisselt

## Homework Statement

I have 2 blocks. M1 is resting on a horizontal plane and attached to a string that goes over a pulley to M2. The plane is like an air hockey table to simulate very little friction. I attached spark tape to M1 so I could measure the time it took and distance traveled. Now, reality and the numbers I got from my equations do not jive:

Test1
m1=.1897kg
m2=.02kg
Distance traveled on plane(X1)=.8462m
Time to travel(X1)=1.5s
actual acceleration =.38m/s^2
predicted acceleration=.9347m/s^2

Test2
m1=.1897kg
m2=.04965kg
Distance traveled on plane(X1)=.7018m
Time to travel(X1)=0.9s
actual acceleration =.87m/s^2
predicted acceleration=2.0329m/s^2

Test3
m1=.2897kg
m2=.04965kg
Distance traveled on plane(X1)=.6797m
Time to travel(X1)=1.2s
actual acceleration =.47m/s^2
predicted acceleration=1.4338m/s^2

## Homework Equations

I used a = m2g/(m1+m2) to predict acceleration

## The Attempt at a Solution

It must be that friction is a factor in this but I do not know how to calculate friction yet. I think it is the normal force of M1 times some constant but I'm not sure how to get it from there. It should be simple but the method escapes me. For instance in test 2 and 3 the set up is identical except I added .1kg to M1 so that I could find some friction value.

thanks for the help

I did some further calculations to find the difference between my predicted acceleration and the actual and found a lost of nearly 60% for each. The 2nd and 3rd trial had only the .1kg difference and the difference between the two was about 10% lost acceleration. Meaning trial 2 lost 57% and 3 lost 67%. Could I say that the friction coefficient is 0.01 (10%) then?

Having said that, this still does not explain where the other lost acceleration went.

can anyone at least tell me if the equation I used to calculate acceleration for this is correct?

I am pretty stuck on this. Right now I'm assuming a reduction of 10% per .1kg. Given that I figured that M1 reduced my acceleration by about 19%. So I'm still missing about 30%. My caliper and scale errors don't even add up to .5%.

## 1. What is the purpose of a simple lab with two blocks and pulley?

The purpose of this lab is to demonstrate the principles of pulleys and how they can be used to lift and move objects. It also allows for the observation and measurement of forces, such as tension and weight.

## 2. What materials are needed for this simple lab?

The materials needed for this lab include two blocks of different weights, a pulley, a rope or string, a ruler or measuring tape, and a weight scale. Optional materials may include a stopwatch and a protractor for more detailed measurements.

## 3. How do you set up a simple lab with two blocks and pulley?

First, attach the pulley to a stable surface, such as a table or wall. Then, tie one end of the rope to the heavier block and thread the other end of the rope through the pulley. Finally, attach the lighter block to the free end of the rope. Make sure the pulley is properly aligned and the rope is taut.

## 4. What are the variables to consider in this lab?

The independent variable in this lab is the weight of the blocks, which can be changed by using different blocks or adding weights to the blocks. The dependent variable is the force required to lift the blocks, which can be measured with a weight scale. Other variables to consider may include the angle of the rope, the coefficient of friction between the rope and pulley, and the speed of lifting.

## 5. What are some possible sources of error in this lab?

Possible sources of error in this lab may include human error in measuring and recording data, variations in the coefficient of friction between the rope and pulley, and external factors such as air resistance. It is important to conduct multiple trials and calculate averages to minimize these errors and obtain more accurate results.

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