Static and kinetic friction example | Forces and Newton's laws of motion | Physics | Khan Academy

TL;DR

When a 5 kg block of wood with a coefficient of static friction of 0.60 is pushed with a force of 100 N, it initially experiences a net force of 70.6 N and accelerates at 14.12 m/s^2. Once the block starts moving, the coefficient of kinetic friction of 0.55 comes into play, resulting in a net force of 73.05 N and an acceleration of 14.61 m/s^2.

Transcript

So I have got this block of wood here that has a mass of 5 kilograms and it is sitting on some dirt and we are near the surface of the earth and the coefficient of static friction between this type of wood and this type of dirt is 0.60 and the coefficient of kinetic friction between this type of wood and this type of dirt is 0.55 This was measured ... Read More

Key Insights

• ❓ The coefficient of static friction determines the force required to start moving an object.
• 🪐 The net force on an object is the difference between the applied force and the force of friction.
• 🖐️ Once an object is in motion, the coefficient of kinetic friction comes into play, affecting the force of friction.
• ❓ The acceleration of an object can differ between the static and kinetic friction scenarios.
• 🖐️ The force of gravity, normal force, and friction all play a role in determining the net force and acceleration.
• 🧑‍🏭 Friction always acts in the opposite direction of motion.
• ❓ The coefficient of friction is a dimensionless value.

Questions & Answers

Q: What is the coefficient of static friction for the block of wood and the dirt?

The coefficient of static friction between the block of wood and the dirt is 0.60.

Q: How does the net force change once the block of wood starts moving?

Once the block starts moving, the net force increases to 73.05 N due to the decrease in the force of friction.

Q: What is the acceleration of the block of wood when it is just starting to move?

When the block is just starting to move, the acceleration is 14.12 m/s^2.

Q: How does the coefficient of kinetic friction affect the motion of the block?

The coefficient of kinetic friction determines the force of friction once the block is in motion, resulting in a net force of 73.05 N and an acceleration of 14.61 m/s^2.

Summary & Key Takeaways

• A 5 kg block of wood with a coefficient of static friction of 0.60 is subjected to a force of 100 N.

• Initially, the block experiences a net force of 70.6 N and accelerates at 14.12 m/s^2.

• Once the block starts moving, the coefficient of kinetic friction of 0.55 comes into play, resulting in a net force of 73.05 N and an acceleration of 14.61 m/s^2.