AAPT.org - American Association of Physics Teachers

# High School Photo Winner's Showcase

« 2012 Winners Gallery

## Balancing Forces by Victoria Elizabeth Kadous

### 2nd Place - Contrived Category

School: Ronald Reagan High School

Teacher: Marie Jo Bolster

In this photo, you can see that the two girls are balancing multiple forces to achieve static equilibrium. The two girls pictured are acrobatic gymnasts performing a skill better known as straddle on bridge. While mounting the skill, the girls have to reach a new center of gravity which is ultimately positioned in the upper torso of the base girl, supported by her two hands and right foot. This requires a shift of balance backwards, while the tension in the leg of the base is resisting the movement backwards until the two gymnasts? momentums successfully counter the other. When the resistance of the base overcomes the momentum of the top girl, the girls reach static equilibrium. At this point, half of the force that both of the gymnasts are exerting is going perpendicular to the floor, while the rest is parallel. If one single force that is being exerted by the girls on the left foot of the base or on ground were to change without the other compensating simultaneously, the skill would collapse in the direction of this unbalanced force. Therefore, by keeping all forces in perfect balance as this picture shows, the acceleration of both of the girls is zero.