lesson1
The title of the laboratory work: Identifying inclined plane efficiency
Purpose of the work:
- Identify the efficiency of the inclined plane with the help of experiment;
- Be aware of and follow the safety rules.
Expected results:
- The total work is greater than the useful work;
- The efficiency is always less than 100%.
Teacher’s Guide:
- Divide the students to 3 students in each group.
- Before starting laboratory work, read the safety rules:
- To download the worksheet, please follow this link:
Theoretical part
The efficiency is defined as the relation between the useful work and the total work. The formula is:
n = Au/At * 100%
where, Au is the useful work, At is the total work.
Sources:
- Простые механизмы. (2019). Физика. Учебник для 7 класса общеобразовательной школы.
- Коэффициент полезного действия (КПД). (2019). Физика. Учебник для 7 класса общеобразовательной школы.
Experimental part
Inclined plane. For this experiment we need an inclined plane, it can be made from scratch using hands on materials. For this purpose, we need hot glue, wooden sticks, cardboard.
Step 1.
Cut rectangular shapes from the cardboard, they will serve as the fundament to the stand. Make cuts in the middle of the rectangles, so that the wooden sticks can fit in.
Step 2.
Use a hot glue to assemble the rectangles and wooden sticks.
Step 3.
Take a bigger piece of cardboard and glue it to the stand. To make the construction more stable, make a cut in the cardboard, stick the stand in the cut and then glue it with the hot glue. Let the hot glue dry before starting.
Experiment.
In this lab we need an inclined plane, dynamometer, measuring tape, weight, pencil, ruler.
Procedure:
Step 1.
Measure the height and the length of the inclined plane. Insert the data to the table.
Step 2.
Identify the force of gravity of the weight using the dynamometer.
Step 3. Calculate the useful work, that is needed to be done to lift the weight:
A1 = F1 h
Step 4.
Hang the weight to the dynamometer and slide them along the plane upwards evenly. Record the force needed and write it down to the table.
Step 5. Calculate the total work:
A2 = F2 l
Step 6. Calculate the efficiency of the inclined plane:
n = A1 / A2 * 100%
Insert the data to the table. Derive a conclusion.
Research part
| № | l, m | h, m | F1 , N | F2, N | A1, J | A2, J | Efficiency, % |
| 1 | |||||||
| 2 | |||||||
| 3 |
When deriving conclusions, answer the following questions:
- What does efficiency show us?
- Why useful work is less than the total work?
Conclusion
The efficiency shows us how efficient the mechanism can be. The useful work is always less than the total work.