# Need help finishing types of forces lab

Lab Assignment 4:  Types of Force

Instructor’s Overview

In many physics problems involving Newton’s laws of motion, you’ll see statements like, “assume a frictionless surface” or “neglecting air resistance…”  In this lab we will be exploring both friction and air resistance, two resistive forces that are critical in the design of real-world products and systems.  Understanding the effects of these types of forces is essential in the design of such things as aircraft, automobiles, braking systems, and countless other objects.

This activity is based on Lab 4 of the eScience Lab kit.  Although you should read all of the content in Lab 4, we will be performing a targeted subset of the eScience experiments.

Our lab consists of two main components.  These components are described in detail in the eScience manual.  Here is a quick overview:

• In the first part of the lab, you will measure the force it takes to pull objects of different mass.  This experiment focuses on the effects of frictional forces.  (eScience Experiment 1)
• In the second part of the lab, you will investigate the effects of air resistance by performing controlled drops of coffee filters.

Notes:

o  Please follow the instructions in this document for the air resistance experiment.

o  Record all of your data in the tables that are provided in this document.

Take detailed notes as you perform the experiment and fill out the sections below.  This document serves as your lab report.  Please include detailed descriptions of your experimental methods and observations.

Experiment Tips and Procedures

Frictional Forces

·  Use the following volumes of water for the three cup types (some of the volumes outlined in the eScience manual are excessive):

 Cup type Volume 1 (ml) Volume 2 (ml) Plastic 300 150 Styrofoam 200 100 Paper 100 50

Air Resistance Procedure – Follow this procedure, not the one outlined in the eScience manual

1.  Take a single coffee filter and flatten it out.

2.  Hold the filter with both hands away from your body at roughly the height of your head.  Measure the drop height.

3.  Practice dropping the filter so that it descends in a reasonably smooth fashion.

4.  Time five (5) drops.  If possible, have a partner help you with the timings.

5.  Enter the drop times in the table provided in this document and calculate the average.

6.  From the average drop time, calculate the average speed of descent.  Show your calculation in the Analysis section of this document.

7.  Use small pieces of tape to stick all of the filters together.  My kit came with three filters.

8.  Repeat steps 1-6 with the “super filter.”

Date:

Student:

Abstract

Introduction

Background:

Objective:

Hypothesis:

Material and Methods

Results

Data tables for the friction experiment:

Plastic cup

 Trial Applied force with 300 ml of water Applied force with 150 ml of water Applied force/Normal force (300ml) Applied force/Normal force (150ml) 1 2 3 4 5 Average

Styrofoam cup

 Trial Applied force with 200 ml of water Applied force with 100 ml of water Applied force/Normal force (200ml) Applied force/Normal force (100ml) 1 2 3 4 5 Average

Paper cup

 Trial Applied force with 100 ml of water Applied force with 50 ml of water Applied force/Normal force (100ml) Applied force/Normal force (50ml) 1 2 3 4 5 Average

Data tables for the air resistance experiment:

Multi-filter

 Trial Drop time (sec) 1 2 3 4 5 Average

Single filter

 Trial Drop time (sec) 1 2 3 4 5 Average

Analysis and Discussion

Friction Experiment

Air Resistance Experiment

Friction experiment

What happened to your applied force Fapp as you decreased the amount of water in the cup?  Explain your answer.

Draw a free body diagram when the applied force is equal to the force of friction (just before the cup begins to slide).  Label the force due to gravity mg, the normal force FN, and the friction force Ff, but don’t use any specific numbers. What makes this a state of equilibrium?

How do the experimentally determined ratios of the applied and normal forces compare between cup types?  What does the ratio of the applied force and the normal force represent?

Look carefully at the force applied right before the cups begin to slide and compare with the force applied as the cup is sliding at constant velocity. Is there a difference in the magnitude of forces? If so, explain. What can you conclude about the coefficients of friction (μs and μk) using the equation Ff=μFN?

Air resistance experiment

Draw a free body diagram for the falling coffee filter. What is the net force?

How would the free body diagram differ for a round rubber ball dropped from the same height?

Are the filters actually traveling at the average speed over the duration of its fall?  Where does the acceleration occur?

Calculate the fall time of the filters assuming no air resistance.  How does this fall time compare with the average fall times of the single and multi-filters?

Why does the combination reach a higher velocity?  To answer this question, use your free body diagram of the falling filter and Newton’s second law to write an equation for the net force on the falling filter.  Solve this equation for the acceleration and note how it depends on the mass of the falling object.

Conclusions

References