Meter Stick Challenge

Using just a meter stick and a 100g weight, we were given the challenge to determine the mass of said meter stick.

The first thing we did was locate the balancing point on the meter stick. We did this by resting the stick on the edge of a table and determining where it balanced on its own, which was about a third of the way up the stick.

To solve, we set up an equation using the formula

 Force x lever arm= Force x lever arm

(Lever arm= distance from axis of rotation)

Note: Convert to Kg.

Use 9.8 for weight

We multiplied the weight (9.8) and lever arm (30) of one side, and set it equal to the weight and lever arm (20) of the other side

Once we got 1.47, we divided by the weight (9.8) to get the weight of the meter stick.

After we found our hypothetical answer, we weighed the meter stick, which ended up being about 146 grams. Since the two numbers are within 10 percent of each other, we know that our process was accurate.

Torques and Basketball

Have you ever wondered why basketball players stand with their legs shoulder width apart with their knees bent? Understanding torques will help us answer this question… A torque is a factor that allows an object to rotate. Torques requires both force and a lever arm. A lever arms are the distance from the axis of rotation Torque= force x lever arm When basketball players are playing ball, it is important that they stand stationary so that they won’t fall over. If they stand with their legs shoulder width apart, they are creating a larger base, and in squatting down, a lower center of gravity. These two factors reduce the chances of a torque occurring because there is no lever arm due to the low center of gravity.

Rotational Inertia and Figure Skating

As you can see in the video, the figure skater spins slower while her arms and leg are extended out, and gains speed as she pulls her limbs in closer to her torso. What causes this change?

Rotational inertia allows an object to resist changes in spinning or circular motion. The factor that affects rotational inertia is not the AMOUNT of mass of the object, but rather the DISTRIBUTION of mass and its location on the object.

That being said, when mass is closer to the axis of rotation the object will have a smaller rotational inertia (easier to move). And when mass is further from the axis of rotation, the object will have a larger inertia (harder to move).

In terms of the ice skater…

While her arms are extended out, her mass is further from the axis of rotation, thus yielding a larger inertia. With the larger rotational inertia, she will move slower. As she brings her arms and leg towards her body, she is bringing her mass closer to the axis of rotation, resulting in a smaller rotational inertia. Hence, she spins faster.