DAY FOUR:
On our fourth visit to Mrs. Dark's Class at Dadeville Elementary School, we taught her second grade class about the center of mass with the following experiments.
First we taught about the basics by saying.. The term gravity is used to describe the force of gravitation on an object on or near the surface of the celestial body, such as the Earth. This force pulls on all mass. All mass exerts a gravitational force, from the smallest subatomic particle to the largest star. The greater the mass, the greater the force of gravity. Center of mass is a point in the object where the mass or weight seems to be concentrated. This point can be in the physical object or some point outside the object. In a round object with equally distributed mass the center of the sphere is the center of the mass. To find the center of mass for an irregular object we would have to do more work.
1) Thumb and chair- Place a chair against a wall so that it cannot be slid back. Have one student sit in the chair with their feet flat on the floor of the chair. Place our thumb on their forehead and ask them to stand up.
-Why can't they stand? It is because their center of mass is still over the seat of the chair not their feet.
2) Are you strong enough? -Place a chair side ways to a wall. Have a student stand so that his or her feet are not under the chair, bend over at the waist and place their head against the wall so that their back is flat. Have them left the chair and then stand up. Have both boys and girls try this. (Be ready to catch the boys!)
-Why can't boys do this? The center of mass for boys is higher than for girls. When a boy is bent over, his center of mass is over the chair and he is balanced against the wall. When he tries to sand he falls. A girl's center of mass is closer to her hips. Even when she is bent over, her center of mass is over her feet, and she can still stand.
3) Leg Lift- One student will stand with their side against the wall with arm and leg touching the wall with nothing to hold onto. Tell them to life the other leg straight out away from the wall.
-Why can't they do this? Same explanation for number 2. This time their upper body can not move to balance them.
On our fourth visit to Mrs. Dark's Class at Dadeville Elementary School, we taught her second grade class about the center of mass with the following experiments.
First we taught about the basics by saying.. The term gravity is used to describe the force of gravitation on an object on or near the surface of the celestial body, such as the Earth. This force pulls on all mass. All mass exerts a gravitational force, from the smallest subatomic particle to the largest star. The greater the mass, the greater the force of gravity. Center of mass is a point in the object where the mass or weight seems to be concentrated. This point can be in the physical object or some point outside the object. In a round object with equally distributed mass the center of the sphere is the center of the mass. To find the center of mass for an irregular object we would have to do more work.
1) Thumb and chair- Place a chair against a wall so that it cannot be slid back. Have one student sit in the chair with their feet flat on the floor of the chair. Place our thumb on their forehead and ask them to stand up.
-Why can't they stand? It is because their center of mass is still over the seat of the chair not their feet.
2) Are you strong enough? -Place a chair side ways to a wall. Have a student stand so that his or her feet are not under the chair, bend over at the waist and place their head against the wall so that their back is flat. Have them left the chair and then stand up. Have both boys and girls try this. (Be ready to catch the boys!)
-Why can't boys do this? The center of mass for boys is higher than for girls. When a boy is bent over, his center of mass is over the chair and he is balanced against the wall. When he tries to sand he falls. A girl's center of mass is closer to her hips. Even when she is bent over, her center of mass is over her feet, and she can still stand.
3) Leg Lift- One student will stand with their side against the wall with arm and leg touching the wall with nothing to hold onto. Tell them to life the other leg straight out away from the wall.
-Why can't they do this? Same explanation for number 2. This time their upper body can not move to balance them.
4) Pick up the Quarter- One
student will stand with his or her back against the wall.
Place the quarter on the floor at their feet and tell them
to pick it up. Most will not be able to do it. Occasionally
a girl with extremely long feet will be able to do with.
-Why is this impossible? When people bend over, their derriere extends to balance them, which keeps the center of mass over their feet. Against the wall an individual's derriere cannot counter balance them.
-Why is this impossible? When people bend over, their derriere extends to balance them, which keeps the center of mass over their feet. Against the wall an individual's derriere cannot counter balance them.