Tree Branch Falling

  On Friday we had a snowstorm that resulted in about 4 inches of very wet heavy snowfall. At some point during the evening, we heard a crash that we first thought was just snow falling off the roof but when we looked out the window, we saw that a large tree branch had fallen- barely missing our car and lamp post in front of our home. So, I was curious about the force of the snow on the branch that made it fall and what would have happened if it had landed on the car instead of next to it. 

To get an idea of what forces were at play, I measured the tree branch, 5.6 m long and 18 cm diameter, and used those numbers plus some research into the density of a typical poplar tree, 385 kg/m³, to find the mass of the tree branch, (Volume x r density = mass) 73.11 kg.  Then I did some research on the density of the snowfall we received that night, 615 kg/m³, and used that to find the weight of the snow, (Volume x r density = mass), 20.99 kg. Next, I calculated the force of the tree branch without the snow, (Force =mass x gravity) 716.5 N, and then the additional force of the snow, 303.8 N. Next, I estimated how far the tree branch fell, about 24 ft or 7.3 m, and use that to find the velocity at which the tree branch fell, (v_f=v_o+at) 11.96 m/s, and use that calculation to find the kinetic energy, (KE=1/2 mv²) 7,446 J. Finally, I used the kinetic energy calculation and guessed how far windshield glass can bend, 0.01 m, and the pressure glass can withstand and found that if the back windshield had been hit, it most certainly would have broken as the tree would have hit it with 29.8 MPa and the glass can only withstand 6.89 MPa. Lucky for us, the tree landed on the lawn!