Help please !!! :) im stuck so if anyone can help that would be lovely!
im doing a lab report and i dont known what the independent varible would be, heres what the lab is about:
Procedures:
Place a clean dry penny on a flat surface.
Fill a small cup of water.
Use a dropper or a pipette to gently drop water onto the penny.
Record the number of drops made before the water spills off the penny.
Dry the penny and repeat steps 1–4. Do three trials.

Explanation:

Materials

Preparation

Place your penny on a flat, level surface that can get a little wet, such as a kitchen counter.

Fill a glass, cup or small bowl with tap water.

Procedure

Fill the medicine dropper with water.

Now carefully add one drop of water at a time to the top of the penny. Hold the medicine dropper just above the top of the penny (not touching it) so each new drop has to fall a short distance before it merges with the drop on the penny. You can write down the number of drops you add if you like. How many drops of water do you think will fit on top of the penny? Watch the drop on top of the penny carefully as it grows. It should keep getting bigger and bigger until it touches the edges of the penny.

Keep adding drops (refill your medicine dropper as necessary) one at a time. How big does the drop on the penny get before it finally spills over the edges?

Once the drop spills over the penny’s edge, use a towel to completely dry off the penny and surrounding surface. How many drops of water were you able to add before the water ran over the penny’s sides?

Mix a small amount of dish soap with your tap water.

Now, repeat the experiment using soapy water. Do you think you will be able to add more drops or less before the liquid spills over the sides of the penny? Again, slowly add one drop at a time. How big does the drop of water on top of the penny get before it breaks and flows over the edges?

Observations and results

You should find that plain tap water produces a much larger, stable drop of water on top of the penny than the soapy water does. This is because plain tap water has higher surface tension, so the surface is "stronger" and can hold together a larger drop. Adding soap lowers the water’s surface tension so the drop becomes weaker and breaks apart sooner. Making water molecules stick together less is what helps soaps clean dishes and clothes more easily.

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