AP Physics 1 - Forces Review

Forces and Motion in Physics

Forces Acting on Objects

• Understanding Forces:
  • When a box is pushed up a ramp, multiple forces act on it, including:
  • Gravitational Force: Downward force due to the weight of the box.
  • Normal Force: Perpendicular to the ramp surface, acting upward.
  • Frictional Force: Acts against the motion up the ramp, varies with the nature of surfaces and is crucial to note.

Acceleration and Friction

• Block and Spring Scale Experiment:
  • A block weighing 80 N is attached to a spring scale, pulled with a scale reading of 32 N.
  • Acceleration Calculation:
  • Use Newton’s Second Law:
    F_{net} = ma
  • Here, net force is obtained by subtracting the spring force from the weight:
    • Net Force: 80 ext{ N} - 32 ext{ N} = 48 ext{ N}
    • Thus, a = \frac{F_{net}}{m}, where m = \frac{W}{g} = \frac{80}{9.8} ext{ kg}.

Motion on Surfaces

• Block on a Flat Surface: When released, if no friction, the acceleration derived from the forces acting on it can be calculated similarly.
• Object on Circular Path:
  • An object moving at constant speed in a circular path experiences centripetal acceleration due to continuous change in direction.
  • It is important to note that despite the constant speed, the object is accelerating due to the change in direction.

Gravitational Forces

• Planet vs. Earth Mass Comparisons:
  • If a new planet has twice the Earth's mass and radius, a person weighing 500 N on Earth would feel a different force:
  • Use the gravitational force formula:
    F = \frac{GMm}{r^2}
  • Analyze the gravitational force changes by adjusting mass and radius.

Satellite Orbits and Forces

• Orbital Motion:
  • For a planet of mass $m$ orbiting a star of mass $M$:
  • Use Kepler’s Third Law, T^2 \propto r^3 for orbital periods to determine relationships.
  • Calculate the specifics of forces and relationship between mass and radius in terms of energy conservation.

Work and Energy in Systems

• Work-Energy Principle:
  • Understand that work done on