Name ____________________________________________ Period ____________
Balanced and Unbalanced Forces Lab
Today you will use blocks of wood, spring scales, and a reference point to model balanced and
unbalanced forces. You will determine the changes in motion that results from each, and calculate
the net force acting on an object.
Materials (per group): block of wood with midline marked on it (and hooks on each end or a string
around it), 1 standard spring scale, 1 push/pull spring scale, and a paper with a straight line with
tape to affix it to the table
Part One:
1. Affix the paper to the table. Place the block so that the midline of the block falls along the
line on the paper.
2. Place a spring scale on each side so that it hooks onto the block hook or string.
3. One person holds the block still over the line while one person on either end picks up the
spring scale on their end (still hooked to the block).
4. The person holding the block counts to 3. At that time, each of the spring scale people use
the scales to pull the block toward them with a force of 20 N. They must keep the force
exactly at 20 N. The person holding the block may then let go.
5. While they are both pulling with 20 N of force, observe the motion of the block.
a. Describe the block’s motion: ______________________________________________
________________________________________________________________________
b. Would you say the forces acting on the block are balanced or unbalanced? Why?
_________________________________________________________________________
Part Two:
1.
Set up the block the same way as in the beginning. Put a spring scale on each end of the
block. The time on the count of 3, each person manning the spring scale will pull on the
object. The spring scale held by the taller person will pull with a force of 20 N, and the spring
scale held by the other person will pull with a force of 10 N.
a. Describe the motion of the block: _________________________________________
_______________________________________________________________________
b. Would you say the forces are balanced or unbalanced? Why?
_______________________________________________________________________
_______________________________________________________________________
Part three:
1. Get with a nearby group to complete the experiment- Set up the block the same way as in the
beginning, but this time put a push/pull spring scale on one end of the block and a regular spring
scale on the other end. On the count of 3, the person manning the push/pull scale will push on
the block with 15 N of force. The person with the regular spring scale will pull with a force of 15
N. Then the person holding the block still will let go.
c. Describe the block’s motion: _____________________________________________
_______________________________________________________________________
d. Would you say the forces acting on the block are balanced or unbalanced? Why?
______________________________________________________________________
______________________________________________________________________
Follow-Up Questions:
1. These kind of forces resulted in the block changing its motion: _______________________
2. These kind of forces resulted in no change in the motion of the block: ___________________
Net force questions:
3. When forces are acting in the same direction, you add them together to get the net force.
For example, if we find these forces 40 N→
→ 20 N, the net force is 60 N →. Calculate
the net force for these scenarios:
25 N ←
← 35 N, net force = _____________________
50 N →
→ 50 N, net force = _______________________
4. When forces are acting in opposite directions, the difference between the two (in the direction
of the stronger force) is the net force.
For example, if we find these forces 20 N →
← 35 N, the net force is 15 N ←. Calculate
the net force for these scenarios:
75 N ←
→ 25 N, net force = _____________________
22 N →
← 56 N, net force = ____________________