HW3_NOTES

Newton's First Law of Motion

• An object at rest will stay at rest, and an object in motion will remain in motion unless acted upon by a net external force.

• Example: A ball traveling on a circular track will continue in a straight line after leaving the track unless a net force is applied.

Motion and Net Force

• Straight Line Path: A moving object, without forces, follows a straight line at a constant speed.

• Hockey Puck Motion: No force is required to keep a hockey puck moving on a frictionless surface, demonstrating that inertia keeps it in motion.

Forces in Constant Motion

• Constant velocity implies that the net force is zero.

• When a girl pushes her brother on a sled at a constant velocity, friction balances the pushing force, meaning the sled's net force is zero.

• Newton's First Law states that zero net force results in constant velocity.

Elevator Motion

• The net force is zero for an elevator moving at a constant speed.

• An object with constant speed in a straight line has zero acceleration due to no net force acting on it.

Basketball Example

• There is zero net force when holding a basketball or after catching it, as its velocity does not change.

• Any velocity change implies a net force acting on the object.

Support Force on an Object at Rest

• A book resting on a table exerts a force of 12N downward due to gravity, so the table must provide an equal upward support force of 12N.

• Net Force: The net force on the book is zero: 12N up equals 12N down.

Scaffold Weight and Forces

• The weight of a scaffold can vary (e.g., 400N, 500N, etc.) but must be balanced by a net force for equilibrium.

Forces Acting on a Bag

• If a bag is pulled down by gravity (18N) and pulled up by a rope (18N), the net force is zero newtons.

Equilibrium of Forces on a Cart

• If a cart is pulled with 100 lbs of force to the right and 30 lbs to the left, the net force is 70 lbs to the right, demonstrating unbalanced forces.

Equilibrium and Constant Speed

• A bowling ball moving at constant speed is in equilibrium (net force EF = 0).

Calculating Net Forces

• Same Direction Forces: A 50N force combined with a 20N force produces a net force of 70N.

• Opposite Direction Forces: A 50N force opposed by a 20N force results in a net force of 30N.

Force Situations Ranking

• Evaluating situations A, B, C concerning force needed to keep objects moving on ice in terms of least to most required force due to negligible frictional forces.