2017 AAPT PHOTO 美国高中生物理摄影大赛国际获奖作品鉴赏！

美国高中生物理摄影大赛由美国物理教师协会AAPT主办，9-12年级的学生，高一至高三学生，GCSE1-A2均合适参加。

This is a photo of a droplet of as it splashed out of a small container of water.There are two things happening.First，the attraction between water molecules allows water to form spherical droplets.This，in turn，creates the second concept，a lens effect.The water droplet acts as a converging lens.As light transfers from one medium to another，air to water，the light encounters a change in density.This change in density，along with the curved surface of the drop，cause the light to change direction.Light transfering from the air to the water drop refracts towards the normal to the surface.It then continues in a straight path to the other side of the droplet.Again，it encounters a boundary between densities.But this time，as light travels from water to air，it refracts away from the normal to the surface.This bending of light creates a focal point that is between the drop and the camera，resulting in a negative focal length，showing an inverted and smaller image.Doesn't physics just make you smile？

This photo demonstrates the principles of center of mass，as a fallen tree has balanced itself across the stump of another.How the tree fell is unknown，but one can see how the weight is distributed evenly acrossthe stump.With more of the tree's length on the right side to balance out the greater girth，and therefore mass，on the left with the base of the tree.The physics behind the phenomenon is ultimately simple.The force due to gravity on either side of the pivot is equal.Due to the nonuniformity of the tree，the center of mass is clearly not the geometric center and could be calculated with simple calculus should the total mass and density of the tree be known.

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