1. Force Purpose  Analyze force vectors in several situations of suspended masses.  Predicting x and y components of forces (Free body diagrams: Done in the homework).  Measuring x and y components of the forces.  Encounter static and dynamic equilibrium situations. Static: acceleration = 0 Dynamic: acceleration  0

2. Force Equipment  Two force sensors (static situations)  One force sensor and one photo gate (dynamic situation)

3. Force Static Suspension of Mass on Strings Force Sensors must be aligned with strings for proper measurement of the force.  Force sensors must be aligned and mass must be temporarily removed while taring the sensor.  Taring must be redone whenever force sensor is realigned.  Tare button is on the side of the force sensor. tare buttons

4. Force WRONG (not aligned) Force sensor will not measure the proper tension in the string.

5. Force Dynamic Situation (Swinging Mass) Photogate at low point of motion Force sensor oriented so string is aligned at low point of motion. Photogate triggers force measurement at the right moment and measures velocity (actually measures time and calculates v).

6. Force Dynamic Situation: Free Body Diagram At the lowest point of the swing: y x W=mg T r a c = v 2 /r (direction of a is in the direction of the net force) (Note: This is just Newton’s second law: F = ma. Only T and W are forces! “ m a c “ is not a force!) mg cos  mg mg sin   

7. Force Data acquisition starts here. This is also the moment in which the mass swings through the photo gate for the first time. Follow instructions Hit the “Scale to Fit” button here if you cannot see oscillations (F <0 if done correctly).

8. Force Hints  In the static situations (no acceleration) we always have:  In the free body diagram the forces must always add up to zero.  For the dynamic situation you need only one force sensor: It must be the force sensor that is plugged into port A of the 750 interface.  Tare the force sensor before you hang the swinging mass on it.

9. Force Hints In Part I you will be asked to calculate the % difference between your measured g and the accepted value of g (use 9.8 m/s 2 for accepted value): In Part III you will also be asked to calculate the % uncertainty in your measurement of tension. With this we actually meant again the % deviation from the expected (calculated) value of T:

10. Force Hints: Measuring the Angle of the String String 90° 60° 30° 0°0° small weight (acts as plumb level)  In this case: Protractor

11. Force Hints: Measuring the Angle of the String – Alternative Method String 90° 60° 30° 0°0°  In this case: