Newton’s first and second laws are vector equations. To use them,

• Draw a free-body diagram.

• Read the x- and y-components of the forces directly off the free-body diagram.

• Use $\sum F_x=m{a}_x$ and $\sum F_y=m{a}_y$.

A net force on an object causes the object to accelerate.

• Identify the forces and draw a free-body diagram.

• Use Newton’s second law to find the object’s acceleration.

• Use kinematics for velocity and position.

《 LOOKING BACK Sections 2.4, 2.5, and 2.6 Kinematics

An object at rest or moving with constant velocity is in equilibrium with no net force.

• Identify the forces and draw a free-body diagram.

• Use Newton’s second law with $\vec{a}=\vec{0}$ to solve for unknown forces.

《 LOOKING BACK Sections 5.1–5.2 Forces

Mass and weight are not the same.

• Mass describes an object’s inertia. Loosely speaking, it is the amount of matter in an object. It is the same everywhere.

• Gravity is a force.

• Weight is the result of weighing an object on a scale. It depends on mass, gravity, and acceleration.

Friction and drag are complex forces, but we will develop simple models of each.

• Static, kinetic, and rolling friction depend on the coefficients of friction but not on the object’s speed.

• Drag depends on an object’s speed and on the Reynolds number.

• Falling objects reach terminal speed when drag and gravity are balanced.

We will develop and use a four-part problem-solving strategy:

• Model the problem, using information about objects and forces.

• Visualize the situation with a pictorial representation.

• Solve the problem with Newton’s laws.

• Review the result to see if it is reasonable.