Force

Question 1

Weight

Answer 1

W = mg

W=wieght

m=mass

g=acceleration of gravity

Question 2

Three Forces on the MCAT

Answer 2

**Gravitational **

• Can act at a distance
• Gravity is usually just mg

Electromagnetic

• Can act at a distance
• Requires a charged object or a magnet

Contact

• Requries visible contact
• The force is either perpendicular (normal force) or parallel (requires friction) to a surface.

Question 3

Newton’s Laws of Motion

Answer 3

Newton’s First Law

• Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it.

Newton’s Second Law

• When an object is acted upon by a net force, the change in that object’s state of motion will be inversely proportional to the mass (m) of the object and directly proportional to the net force (F) acting upon the object.

F = ma

​Newton’s Third Law

• For every action(force) there is an equal and opposite reaction. These forces never act on the same system(mass).

Question 4

Force

Answer 4

Force is equal to mass times acceleration

F = ma

Question 5

A Newton (N)

Answer 5

1 N = (1 kg)(1 m/s²)

Question 6

Newton’s Law of Universal Gravitation

Answer 6

G = 6.67 x 10^-11 m³kg^-1s^-2

Question 7

Inclined Planes

Answer 7

• The net force due to gravity and the normal force of an inclined plane is always equal to mg sinØ and points directly along the plane.
• mg sinØ is the sum vector.
• The normal force is always mg cosØ

​

F = mg sinØ

F_n = mg cosØ

Question 8

Inclined Plane (Curved Surface)

Answer 8

The normal force for a mass moving down a curved surface has two jobs:

• a protion (mg cosØ) counters some gravitational forces
• the rest (mv²/r) creates the centripetal acceleration to change the direction of the velocity.

The normal force in this case is (mg cosØ + mv²/r)

Question 9

Circular Motion

Answer 9

• Acceleration and Force point toward the center of the circle.

Question 10

Static Friction

Kinetic Friction

Answer 10

Contiguous surfaces may exert equal and opposite forces against each other parallel to their contiguous surfaces. If the surfaces do not slide relative to each other, the force is static friction. If the surface slides relative to each other, the force is kinetic friction.

Question 11

Tension

Answer 11

• Treat tension as a force pulling away from an object

Question 12

Hooke’s Law

Answer 12

• k is the “spring constant” unique to the object.
• (-) indicates that the force is in the opposite dircetion of the displacement.