Skip to content
Dabour HubLEARN · PRACTICE · EXPLORESign inStudent

2.6Force and Translational Dynamics

Gravitational Force — AP PHYSICS 1 Revision Notes & Topical Questions

5 min read 9 parts Lesson 22 of 36 1 quiz

📚 AP PHYSICS 1 Hub / Topical Revision
🩺
100% Curriculum Specification Match Lesson Doctor Verified
The only platform with 100% curriculum specification match and verified interactive question banks.
0%read
Lesson summary

2.6 Gravitational Force — AP PHYSICS 1 notes: Describe Newton's law of universal gravitation, the gravitational field, free fall, weight and apparent weight.Law — Fg = Gm1m2/r2G = 6.67 × 10-11 N m2 kg-2.r is the distance between the centers of mass.Inverse square law — doubling t…

  • Attractive
  • Field lines
  • Radial field
  • Uniform field
  • Field strength
  • Mass versus weight

Section 1 of 9Newton's law of gravitation

Law
  • Fg = Gm1m2/r2
  • G = 6.67 × 10-11 N m2 kg-2.
  • r is the distance between the centers of mass.
Inverse square law
  • Inverse square law doubling the distance divides the force by 4
Spheres
  • Spheres a uniform sphere acts as a point mass at its center

Section 2 of 9Nature of gravitational force

Attractive
  • Attractive always pulls masses together along the line joining their centers of mass
Range
  • Range infinite
Orbits
  • Orbits gravity provides the centripetal force for the Moon and satellites

Section 3 of 9Gravitational field

Field
  • Field region where a mass experiences a gravitational force
Field lines
  • Field lines show direction toward the center of the attracting mass; their density shows strength
Radial field
  • Radial field non-uniform, strength depends on distance
Uniform field
  • Uniform field near Earth's surface, g = 10 N kg-1

Section 4 of 9Field strength and free fall

Field strength
  • Field strength g = Fg/m = GM/r2
Free fall
  • Free fall a = g = 10 m s-2 independent of mass when air resistance is negligible

Section 5 of 9Weight

Weight
  • Fg = mg, the gravitational force from a nearby astronomical body
Mass versus weight
  • Mass versus weight mass is the same everywhere; weight depends on g

Section 6 of 9Apparent weight

Apparent weight
Apparent weight
  • Apparent weight the magnitude of the normal force on the object
Elevator accelerating downward
  • FN = mg − ma, so apparent weight is less
Elevator accelerating upward
  • FN = mg + ma, so apparent weight is more

Section 7 of 9More from the specification

More from the specification
Buoyant force
  • Upward force equal to the weight of displaced fluid.
Equivalence principle
  • Acceleration and gravity are indistinguishable locally.
Constant
  • Not changing.
System
  • Objects analysed together.
Reference frame
  • Coordinate system used by an observer.

Section 8 of 9Key terms

TermMeaning
Newton's law of gravitationF = Gm1m2/r2.
Gravitational field strengthForce per unit mass, g = GM/r2.
WeightGravitational force on a mass.
Apparent weightNormal force on an object.
Free fallMotion under gravity alone.

Section 9 of 9Exam technique

1
Using the surface-to-surface distance for r.
2
Forgetting to square r.
3
Equating weight and mass.
4
Saying gravity is zero for astronauts in orbit — they are in free fall.

Last updated: