2 Forces and Newton’s Laws Free Online FlashCards

What are the defining features and SI unit of force?

Force is a vector interaction that can change an object’s velocity. Its SI unit is the newton $N$, where $1\,\text{N}=1\,\text{kg·m/s}^2$.

How is net force found?

The net force is the vector sum of all forces acting on the object: $\vec F_{\text{net}}=\sum_i\vec F_i$.

How do you resolve a force into x- and y-components?

For a force $F$ at angle $\theta$ above the positive x-axis, $F_x=F\cos\theta$ and $F_y=F\sin\theta$.

What belongs on a free-body diagram?

An FBD isolates one object and shows every external force acting on it. Do not include forces the object exerts on other objects or add net force as another force.

What does Newton’s first law say when net force is zero?

In an inertial frame, zero net external force means an object stays at rest or moves with constant velocity. Its acceleration is zero, but its velocity need not be.

What relationship does Newton’s second law give?

Newton’s second law is $\vec F_{\text{net}}=m\vec a$. Acceleration points in the direction of net force; for a given force, greater mass means smaller acceleration.

What does Newton’s third law say about an interaction pair?

If object A exerts a force on object B, B simultaneously exerts an equal-magnitude, opposite-direction force on A. The two forces act on different objects.

What condition defines translational equilibrium?

Translational equilibrium requires $\vec F_{\text{net}}=\vec 0$, so $\vec a=\vec 0$. The object may be at rest or move with constant velocity.

What is an object's weight?

Weight is Earth’s gravitational force on an object: $\vec w=m\vec g$. Near Earth’s surface, it points vertically downward and is measured in newtons.

What is the normal force, and how is it directed?

The normal force is a contact force perpendicular to a surface. Its magnitude is not automatically equal to the object’s weight.

How is tension directed on an object?

Tension is a pulling force transmitted by a taut cord or rope. It acts along the cord and away from the object.

What does Hooke’s law say about an ideal spring force?

An ideal spring exerts $\vec F_s=-k\vec x$, where $\vec x$ is displacement from its relaxed position and $k$ is stiffness. The minus sign indicates a restoring force.