Physics Involved- Projectile Motion, Action-Reaction Force Pairs, Gravitational Potential Energy
Today we will explore Box Jumps and the physics of moving through the air from the ground to the box, Kinematics, three laws, projectile motion and falling back down and energies associated with this exercise. Box Jumps use the strength in ones legs to fight the force of gravity and bring self up to above box height and over onto it. Forces involved are Fg and a normal force plus friction and Normal force. The force of gravity weighing down the person is combated by the force of a persons legs pushing up and the force of Friction is overcome by a person pushing them self towards the box. Here we will be showing the physics behind someone jumping. Jumping is using your legs to go up and forward to land on top of the front of a box. The Kinematics are simple. You stay at a constant speed until you land on the box and are stopped. So acceleration is always 0 on the x-axis. The inertia is the mass you are pushing (yourself). You will have forces to deal with. The force of gravity on the mass you are lifting (you). You will not hit free-fall because you are stopping at a higher place then where you start. In this exercise the relation ship between initial speed and range is proportional. As Vi increases the distance away where you will land is further and with a smaller Vi you will not go as far. As the angle increases the range decreases because it is a higher height reached but less of a range. Depending on the initial speed you will be higher or lower in this exercise. The more you push, the faster you will be at the start and the higher you will go. If you want to go higher your launch angle should be more vertical than horizontal.
Today we will explore Box Jumps and the physics of moving through the air from the ground to the box, Kinematics, three laws, projectile motion and falling back down and energies associated with this exercise. Box Jumps use the strength in ones legs to fight the force of gravity and bring self up to above box height and over onto it. Forces involved are Fg and a normal force plus friction and Normal force. The force of gravity weighing down the person is combated by the force of a persons legs pushing up and the force of Friction is overcome by a person pushing them self towards the box. Here we will be showing the physics behind someone jumping. Jumping is using your legs to go up and forward to land on top of the front of a box. The Kinematics are simple. You stay at a constant speed until you land on the box and are stopped. So acceleration is always 0 on the x-axis. The inertia is the mass you are pushing (yourself). You will have forces to deal with. The force of gravity on the mass you are lifting (you). You will not hit free-fall because you are stopping at a higher place then where you start. In this exercise the relation ship between initial speed and range is proportional. As Vi increases the distance away where you will land is further and with a smaller Vi you will not go as far. As the angle increases the range decreases because it is a higher height reached but less of a range. Depending on the initial speed you will be higher or lower in this exercise. The more you push, the faster you will be at the start and the higher you will go. If you want to go higher your launch angle should be more vertical than horizontal.
The only connection between the x and y component in this exercise is the time variable. The trajectory is almost a full parabola but it has an abrupt stop when you land on the box. In this exercise we see how the jumper is counteracting the effects of gravity on the system with the normal force from his legs. The gravitational force of the earth on him downward has an equal and opposite reaction force of the gravitational force of the jumper on the earth upwards. The normal force of the floor on the legs upward has an equal and opposite reaction force of the normal force of the legs on the floor downward. The normal force of the floor on the legs to the right has an equal and opposite reaction force of the normal force of the legs on the floor left. The friction force of the floor on the legs to the left has an equal and opposite reaction force of the friction force of the legs on the floor to the right. At the very top he hits a falling motion called free fall that brings him back down to the box. This is free fall. Gravity sends him down at -9.8m/s squared. In this exercise we see how the jumper is affected by energies. The first part, which is the going down part, is work into the system. After, his movement up is Kinetic Energy because he is moving. Before he goes down he hits the peak where v = 0. At this point he is being influenced only by GPE energy. As he starts to come down there is more kinetic energy. The forces are normal forces and gravity. At the end of the exercise when he stops moving there is work out. To do this you need a box and some legs. These legs must work.
Here's a YouTube clip in case you're having trouble figuring it out. Try and spot the physics going on:
Here's a YouTube clip in case you're having trouble figuring it out. Try and spot the physics going on: