HW_4_NOTES

Page 1: Newton's Laws of Motion and Forces

• Acceleration and Net Force

  • Acceleration is proportional to the net force.

  • To drag a block across a table, a steadily increasing force must be applied. Example: Dr. Hewitt applies 3N of force to keep the block moving steadily; the opposing force from friction must exactly balance this, meaning the friction is also 3N.

• Friction

  • When dragging a block at a steady speed of 2 m/s with a force of 5N, the friction must be 5N to allow for a constant velocity.

  • General conclusion: The force needed to keep an object moving at a steady rate equals the frictional force opposing it.

• Static vs. Sliding Friction

  • Static friction is normally greater than sliding friction for the same object.

  • To keep an object moving against friction, a push must always oppose the sliding friction.

Page 2: Understanding Forces and Motion

• Effects of Mass and Applied Force on Acceleration

  • If the mass of an elephant is increased, acceleration decreases. Conversely, increasing the applied force increases acceleration.

• Newton's First Law

  • An object at rest stays at rest unless the net force acting on it is zero.

  • A block moving at a constant velocity has a net force of zero acting on it; either no forces are acting on it, or they cancel out.

• Newton's Second Law

  • If a 2kg block is subject to forces resulting in 4N, it can move left, right, or at rest.

• Free-Falling Objects

  • In free fall, both heavy and light objects have the same acceleration due to gravity, and their weight-to-mass ratio is consistent.

Page 3: Forces in Different Contexts

• Factors Affecting Air Resistance

  • Air resistance relies on the surface area and speed of the falling object.

• Weight Calculation

  • Weight of a 1900 kg elephant: Weight (W) = mass (m) x gravity (g) = 1900kg x 10m/s² = 19,000N.

• Acceleration of Objects

  • The acceleration experienced by objects can vary based on mass and applied net forces.

• Ranking Objects and Forces

  • Ability to rank net forces and accelerations based on applied force or mass.

Page 4: Dynamics of Force and Mass

• Effect of Mass on Acceleration

  • Doubling the mass while applying a constant net force halves the acceleration.

• Net Force Calculation

  • For a 200kg refrigerator pushed with a force of 4N, the acceleration can be calculated using F=ma.

• Effects of Applied Forces

  • If applied force goes to zero, acceleration also becomes zero, keeping velocity constant unless acted upon by friction.

Page 5: Friction and Inclination Forces

• Static Friction on Ramps

  • As the ramp angle increases, static friction must match the component of gravitational force acting parallel to the ramp.

• Maximum Ramp Angle

  • The maximum angle for static friction to hold steady relates to the coefficient of friction and must not exceed certain thresholds.

Page 6: Free Body Diagrams and Forces

• Understanding Forces

  • Free-body diagrams illustrate forces acting on different objects, such as friction and normal forces.

• Force and Acceleration in Action

  • Under Newton's third law, forces occur in equal and opposite reactions between interacting objects.

• Distance Traveled by Objects

  • The bullet from a rifle travels farther due to its greater acceleration compared to the rifle, but both experience equal magnitudes of force.

Page 7: Force Interaction with Earth

• Weight on Earth

  • While pulling on Earth, it is essential to recognize that this action also creates an equal force back on the person pulling.