Credit: https://phet.colorado.edu/sims/html/forces-and-motion-basics/latest/forces-and-motion- basics_en.html Objective:

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Credit: https://phet.colorado.edu/sims/html/for ... nd-motion- basics_en.html Objective: Through this virtual lab assignment/simulation, friction force acting on an object will be examined for three different situations: stationary object, impending motion situation, and moving object. Static friction coefficient and kinetic friction coefficient values will be calculated. Theory: When a force P is applied to an object supported on a horizontal surface, a resistive force called friction force (F) is developed, that opposes the motion or tendency of motion. The free-body- diagram of such an object is shown below. The friction force, F increases as the applied force, P is increased and F is equal and opposite to P, but up to a certain limit. In the impending motion situation F is equal to Fmax (= HsN). If the applied force is increased beyond the Fmax value, then the object starts to move, and also the friction force is reduced a little bit. In other words, kinetic friction (F) is less than the maximum static friction, Fmax. The kinetic friction coefficient is defined according to the following equation: Fx = μxN. W P Static friction Impending motion (F max) Kinetic friction F=P Figure 1(b) Variation of friction force (F) with the applied force (P) N Figure 1(a) Free-body-diagram of the block
Lab narrative: 1. Copy and paste the following URL in your browser: https://phet.colorado.edu/sims/html/for ... nd-motion- basics en.html 2. Click on the "Acceleration" tab. Case 1: Moderate friction coefficient (default setting) 3. Check all the boxes in the top right corner (Forces, Sum of forces, Values, Masses, Speed, Acceleration) 4. Do not slide the friction control slider (i.e., keep it exactly in the middle or default position. If you move it, then hit the reset button to bring it exactly in the middle. If you slide it manually, it is very difficult to know if it is exactly in the middle or not). This will set the static friction coefficient to a fixed moderate value. 5. Drag and bring the m-50 kg block on the surface. Note: it might be already in that location.
6. Click on the right arrow (single arrow) under "Applied force". You will notice the force value increases from 0 N to 1 N, 2 N, and so on. 7. Notice the "Applied force" and "Friction force" values. Notice the "Sum of forces" value for the vector sum of the two. 8. Keep on increasing the "Applied force" till you reach the maximum applied force for which the "Applied force" is equal to the "Friction force". That is the maximum value of friction possible (and the block does not slide yet). Note it down. (Note: if you increase the applied force by 1 N, the friction force drops, and the block slides) Fmax = N 9. Calculate Us-Fmax/N, Note: you will need to determine normal force, N. U₂= 10. Increase the "Applied force" by 1 N. Notice that the block starts to move and the "Friction force" has a reduced value. This is the kinetic friction force. Note this applied force, P and kinetic friction force Fx values. Note the "Sum of forces". Check if "Sum of forces is indeed equal to (P-F). Also, note the "Acceleration value". P= N Fk= N Sum of forces P-Fx = Acceleration reading m/s² Calculated acceleration = (P-F)/m= m/s² 11. Calculate uk-Fi/N Case II: Large friction coefficient (friction- "lots") Repeat steps 3-11 for the same block (m= 50 kg), but with maximum setting for the "Friction" (by selecting the max or "lots" value from the slider in the top right corner). Note the corresponding values, and calculate the friction coefficients (Show calculations):
Static Friction: Fmax = Hs F Kinetic Friction: P= N Fk= N Sum of forces P-Fk= Acceleration reading= Calculated acceleration= (P-F)/m= m/s² =Fx/N= Discussions: 1) How does the maximum static friction force and kinetic friction force vary with the friction coefficients (for a given mass of block)? 2) Do you think the maximum static friction force depends on the surface area of contact? N N m/s²