Lesson 4.15: Vector Analysis and Forces Acting on an Object
Aug 13, 2024
Lecture Notes: Physics of Friction and Motion
Introduction
Discussion on a block of wood with a mass of 5 kilograms on dirt near the Earth's surface.
Coefficients of friction:
Static friction: 0.60
Kinetic friction: 0.55
Force applied: 100 Newtons
Concepts of Motion Without Friction
If no friction existed:
Only the 100 Newton force would act.
Net force = 100 Newtons.
Formula: Force = Mass x Acceleration (F = ma).
Acceleration = Force/Mass = 100 N / 5 kg = 20 m/s² (rightward).
Understanding Friction
Static Friction: The force needed to start moving an object.
Kinetic Friction: The force acting against motion once the object is moving.
Friction is always opposing the direction of applied force.
Normal Force: Equivalent to gravitational force when the block is stationary (49 Newtons).
Calculations for Static Friction
Budging Force: Force needed to overcome static friction.
Gravitational Force: 9.8 m/s² x 5 kg = 49 Newtons down.
Normal Force: Balances gravitational force = 49 Newtons up.
Budging Force Calculation:
49 Newtons x 0.60 = 29.4 Newtons.
100 Newtons is sufficient to overcome static friction.
Transition from Static to Kinetic Friction
Static Friction: Initial net force = 100 N - 29.4 N = 70.6 N (right).
Acceleration: 70.6 N / 5 kg = 14.12 m/s² (right).
Kinetic Friction: Starts once the block is in motion.
Calculations for Kinetic Friction
Kinetic Friction Force: 49 N x 0.55 = 26.95 Newtons.
Net Force when moving: 100 N - 26.95 N = 73.05 Newtons (right).
Acceleration when moving: 73.05 N / 5 kg = 14.61 m/s² (right).
Key Takeaways
Overcoming static friction requires more force than maintaining motion due to kinetic friction.
Initial acceleration is slightly lower due to static friction, but once moving, acceleration increases due to lower kinetic friction.
Understanding these principles is crucial for analyzing motion and force interactions in physics.
Conclusion
The lecture provides an in-depth understanding of how friction affects motion and the calculations involved in predicting the behavior of objects subject to forces on Earth.