Science fair projects are often required for seventh-grade students. Though erupting volcanoes and electrical circuits are two popular projects, some schools prohibit these overused themes in hopes that seventh-grade students will choose unique ideas and test proven theories. Science fair ideas for seventh-graders can be completed in as little as one day, but winners often take longer.

If the science fair is tomorrow, all hope is not lost. A few science fair projects can be completed in less than 24 hours with items from around the house.

Questions that can be answered in one day or less: Does the shape of ice affect how fast it melts? Does salt make water boil faster? Which type of soda has the lowest pH? Does fresh water, tap water or salt water have the lowest pH?

For seventh-graders who have waited until nearly the last minute, one-week project topics are the right choice. The shorter time line does not allow for building working machines or growing plants. Some theories, however, can be tested in a week.

Questions that can be answered in one week: Does body temperature change by the hour? Do objects fall faster when dropped from higher starting points? Does water slow down a tennis ball? Do drivers follow the speed limit?

Projects that take about one month include observations, questionnaires, polls and plants. Though many science fair projects in this category can be completed in less than four weeks, seventh-graders should allow extra time for gathering data and presenting data in a research paper.

Questions that can be answered in one month include: Will food coloring change the color of plant blossoms? How does athletic participation affect grade point average? Are girls smarter than boys?

Any science fair project that involves growing plants should be started more than one month in advance of the science fair. Some seeds require six to eight weeks or more to grow. This is especially important if you're growing flowers; the plant may grow in a month, but flowers may not bloom for another few weeks. Building a working machine may also take more than one month, allowing time to order and receive parts.

Questions that can be answered in more than one month include: Does water salinity affect plant growth? Can plants grow in a vacuum? Will magnets generate electrical energy? How much energy does a wind turbine generate?