Well there are quite a lot of science projects that can win you a prize
for example: make a model based on the principle of hydraulics. you can get the materials to make this project in hobby ideas. you can also make a project based on the newtons 3rd law: every action has an equal and opposite reaction that is a pop-pop boat. you can get to know how to make it in youtube: go on www.youtube.com and write pop-pop boat. you can either choose the first option that appears or the fourth option that appears. I would prefer the fourth option [every thing you need to know about pop-pop boats because that method is more durable. you can also make a solar cone or developing energy from house-hold products like salt mixed with water by putting copper and zinc plates which are connected with wires that are attached to a bulb or a digital clock, using potatoes or apples or lemons in the same manner. ALL THE BEST!!!!!