Spring Discovery Lab
Materials
Assorted spring-scales Assorted strings looped at each end
Mass-set & (2) hangarsVertical & Horizontal Rods
Purpose
Learn about how springs measures force.
1. Does a spring measure one force or two?
A. Lay one of your spring-scales on the table. Pull on the bottom hook without pulling on the top hook. Can you get the scale to read a steady 2N force? ____ Why not? ______
B. Now pull gently on both ends of the spring-scale. Can you get the scale to read a steady 2N force? ____ Why? ______
C. Attach the top end of the spring-scale to a rigid object. Pull on the bottom hook till the scale reads 2N. How many forces act on the spring-scale in this situation? ______Does the rigid object pull on the spring-scale? _____ If so, how large a force is it pulling with? ______
2. Is the tension ever different at different places in a string?
A. Attach the bottom hook of a 5N and a 10N spring-scale to a length of string. Pull so that one scale reads 2N. What does the other scale read? ______Pull so that one scale reads 5N. What does the other scale read? _____
B. Get 3 scales for this part and two lengths of string. Put one scale in the middle and attach a length of string to each end of it. Hook the bottom hook of the other scales to the other end of each string. Pull so that one of the end scales reads 2N. What do the other two scales read? ______Pull so that one of the end scales reads 5N. What do the other two scales read? ______Is the force in the middle different than the force at the ends?
3. Measuring weight.
A. Zero two spring-scales when held vertical. Hang one spring-scale from a horizontal rod so the bottom hook is down. Hang another spring scale from the bottom of the top scale. What does the top scale read (look carefully)? ______What does the bottom scale read? ______What object is the top scale weighing? ______What object is the bottom scale weighing? ______
B. Keep the same arrangement as above. Hang a 200 gram mass from the bottom scale. What does the top scale read? ______What does the bottom scale read? ______What object(s) is the top scale weighing? ______What object(s) is the bottom scale weighing? ______
Would the bottom scale read the same if it were held from a rod instead of from the top scale? ______Try it and see what happens.
C. Get two identical masses (e.g. 200 grams) and two identical mass hangars. Hold a spring-scale firmly on the table. Hook a string from its bottom hook and let the other end of the string hang over the table. Hang one of the masses from the string. What does the spring-scale read? ______Now attach a string to the top of the spring-scale that is long enough to hang over the other end of the table. Hold onto the spring-scale while you hang the second identical mass from this string. You should be able to let go of the spring-scale and not have it move much. Tap the spring-scale lightly to even up the friction on each side of the scale. What does the spring-scale read? ______Does the spring-scale measure the weight of both masses or just one? ______
Summing Up
When a secured spring-scale is reading a force of 5N, how large is the securing force? ____
You pull with 5N on one end of a string, and your partner pulls with 5N on the other end. How large is the tension force in the center of the string? ______
Can an unsecured spring-scale be used to measure a force? ______
Does the type of object used to secure a spring-scale affect how it works? ______