Treating systems (the easy way) | Forces and Newton's laws of motion | Physics | Khan Academy

TL;DR

By treating a system of objects as a single object, you can find the acceleration by dividing the sum of the external forces by the total mass.

Transcript

• [Voiceover] So in the previous video we solved this problem the hard way. Maybe you watched it, maybe you didn't, maybe you just skipped right to here and you're like, "I don't even wanna know the hard way. "Just show me the easy way please." Well, that's what we're gonna talk about now. Turns out there's a trick and the trick is after you solve ... Read More

Key Insights

• 👻 Treating a system of objects as a single object allows for a simple and quick calculation of acceleration.
• ❓ Only external forces contribute to the acceleration, while internal forces cancel each other out.
• ❎ The direction of the forces determines whether they are considered positive or negative in the calculation.

Questions & Answers

Q: How can you find the acceleration of a system of objects?

To find the acceleration, treat the system as a single object and divide the sum of the external forces by the total mass of the system.

Q: Do internal forces affect the acceleration of the system?

No, internal forces, like tension, cancel each other out and do not contribute to the acceleration of the system.

Q: How do you determine which forces make the system go?

Forces that are directed in the same direction as the motion of the system are considered positive and contribute to the acceleration. Forces that resist the motion of the system are negative.

Q: What is the significance of dividing by the total mass?

Dividing the sum of the external forces by the total mass gives the measure of inertia of the system and determines how much the system resists changes in velocity.

Summary & Key Takeaways

• The trick to finding the acceleration of a system of objects is to treat the system as a single object and divide the sum of the external forces by the total mass.

• Internal forces, such as tension, cancel each other out and do not contribute to the acceleration of the system.

• The acceleration of the system depends on the forces that make the system go and the forces that resist the motion of the system.