Exploring Vectors

Introduction

Vectors are quantities that have direction as well as magnitude. Some examples of vectors are velocity, displacement, force and acceleration. Direction is an important component in physics as you can readily understand if you consider forces. The direction that a force is applied makes a huge difference on the motion of the object. Suppose that computer cart is rolling down the hallway in an easterly direction. If a net force is applied to the cart in the same direction the cart is rolling, the cart will roll faster toward the east. If the same net force is applied to the cart in a westerly direction, the cart will slow down. If the net force is applied in a southerly direction, the cart will begin to turn toward the south. Direction matters.

Purpose

To investigate how direction makes a difference when applying forces.

Materials:         

• three spring scales (20 N if possible)
• a short piece of string ≅ 10 cm
• a longer piece of string ≅ 1 m
• a 500 g or 1000 g hook mass

Procedure

Make a loop out of the small string by tying its ends together. Suspend the mass from the string using the two spring scales. The hook of each spring scale should also be attached to the string. Lift the mass with an straight upward force from each spring scale at the same time. Record the readings. Try lifting the mass again using the spring scales, but this time pull about 15o to the right of straight up with one scale and with the other pull about 15o to the left of straight up. Record the force required by each scale. Continue to vary the angle and record the forces each time. Construct a chart to organize your data. Draw two relevant conclusions.

Obtain a piece of string about a meter long. Tie a small loop in each end so you are able to attach one spring scale hook to each loop. With the help of a couple friends, one on each end of the string, pull on the ends of the string to make the string horizontal. The hooks on the spring scales should be pointed toward each other. Using a third spring scale, hook it near the middle of the horizontal string and pull downward. Have your friends keep the string as horizontal as possible while you vary the force you pull down at the middle of the string. Make observations, collect some data, and draw a conclusion.

Discussion questions

1. Why does pulling straight up with the spring scales result in less force to lift the mass?

2. Explain in your own words why lifting the mass while pulling to the side of straight up requires more force?

3. Why do clothes hung near the middle of a clothes line, no matter how taut the line, always cause the line to sag?

Image source