PYL 105

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Forces in Equilibrium

If an object is neither moving through space (translating) nor rotating, it is said to be in static equilibrium. The sum of the external forces acting on the object must be zero (recall forces add as vectors); and similarly the sum of the external torques must be zero.

The forces in this lab will be tensions and weights. The magnitude of the weights will be determined by using known masses and using the formula mg. Furthermore, the direction of weight is known to be vertically down. Because the masses are in static equilibrium, we will be able to determine (most of) the tensions. Next, we will use pulleys to change the directions of the tensions. The new direction of the tensions will be observable since tensions act along the string. Using a protractor to measure angles (directions), we can apply the ideas of vector addition, i.e. choosing a coordinate system, breaking forces into components in that coordinate system, and adding the components, to test our notion of equilibrium and then to use it to determine unknown forces.

A Force Sensor (a type of spring balance) can be used to measure forces. In the third part of the lab, we test a Force Sensor using known weights. In the last part of the lab we will use the pulley as a simple machine.

Part 1: Confirming equilibrium

 

Part 2: Using equilibrium to find unknowns


Part 3. Calibrating the Force Sensor.

Do you observe any errors in your force sensor readings? If so, are they systematic or random? Explain.

Part 4 Pulley Effect

Arrange your apparatus based on the figure below. When W1 (hanger and added mass) has a mass of 100g what is the sensor's reading? Repeat with 150g, 200g and 250g. What is the sensor holding up? With the 250g attached slowly pull the force sensor 4cm. By how much does W1 move?

Pulley as simple machine

Mass (kg) Force (N)
0.100  
0.150  
0.200  
0.250  
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