Grade 11 Physics - Static and Kinetic Friction Example

Summary

This video provides a detailed explanation of how to calculate the coefficients of static and kinetic friction through a multi-part example. The scenario involves a box filled with IV bags being dragged across a horizontal floor. Key steps include calculating the total mass of the box and IVs, finding the static and kinetic friction coefficients, and addressing the impact of applied forces on friction. The video also demonstrates how friction behaves when forces are applied to move a stationary box and how to find the coefficient of kinetic friction when the box is accelerating.

Takeaways

• 😀 The example involves calculating the coefficient of static and kinetic friction for a box filled with IV bags dragged across a horizontal floor.
• 😀 The box contains 25 IV bags, each with a mass of 250 grams, and the box's own mass is 2.8 pounds.
• 😀 To solve the problem, the mass of the IV bags must be converted from grams to kilograms (250 grams = 0.25 kg per IV bag).
• 😀 The total mass of the box with the IV bags is 7.52 kg, derived by adding the mass of the IV bags and the box.
• 😀 The weight of the box (force of gravity) is calculated by multiplying the mass by 9.8 m/s² (gravity).
• 😀 The force required to move the box is 59 N, which is used to calculate the coefficient of static friction.
• 😀 The coefficient of static friction is determined by dividing the maximum static friction (59 N) by the normal force (73.07 N), yielding a value of 0.80.
• 😀 For part B, the coefficient of kinetic friction is calculated using the force required to keep the box moving at a constant speed (35 N), resulting in 0.47.
• 😀 For part C, if 35 N is applied to the box while it's stationary, the force of friction matches the applied force of 35 N since it's below the threshold for motion (59 N).
• 😀 Part D involves finding the coefficient of kinetic friction when the box accelerates at 0.4 m/s² under an applied force of 33 N. The coefficient is calculated after determining the net force and friction force.

Q & A

What is the scenario described in the example?

The example describes a box filled with 25 IV bags, each weighing 250 grams, which is being dragged across a horizontal floor.

What is the mass of the IV bags in kilograms?

The mass of each IV bag is 250 grams, which converts to 0.25 kilograms. With 25 IV bags, the total mass of the IVs is 6.25 kilograms.

How do you calculate the weight of the box in Newtons?

The weight is calculated by converting the mass of the box from pounds to Newtons. The box weighs 2.8 pounds, which converts to approximately 12.44 Newtons.

What is the total mass of the box and IV bags combined?

The total mass is the sum of the box's mass (1.27 kg) and the mass of the IV bags (6.25 kg), giving a total mass of 7.52 kg.

What is the force required to overcome static friction and move the box?

The force required to overcome static friction and move the box is 59 Newtons, which is the maximum static friction force.

How do you calculate the coefficient of static friction?

The coefficient of static friction is calculated by dividing the maximum static friction force (59 Newtons) by the normal force (73.07 Newtons), which results in a coefficient of approximately 0.80.

What happens if a force of 35 Newtons is applied to the box?

If 35 Newtons is applied to the box when it is stationary, the box does not move because the static friction force is greater than the applied force. The friction force will exactly match the applied force to prevent motion, keeping the friction at 35 Newtons.

What is the coefficient of kinetic friction when the box moves at a constant speed?

When the box moves at a constant speed with a force of 35 Newtons, the coefficient of kinetic friction is calculated as 0.47 by dividing the kinetic friction force (35 Newtons) by the normal force (73.07 Newtons).

How do you calculate the coefficient of kinetic friction when the box is accelerating?

To calculate the coefficient of kinetic friction when the box is accelerating, you use Newton's second law. First, calculate the net force (applied force minus kinetic friction force). Then, using the acceleration and mass, find the frictional force and divide it by the normal force.

How do you find the force of kinetic friction when the box is accelerating?

The force of kinetic friction is found by using Newton's second law. First, subtract the net force (33 Newtons applied force minus 3 Newtons from acceleration) from the applied force to find the kinetic friction force, which is 30 Newtons.