4 - Newton’s Laws of Motion Free Online FlashCards

What is net force?

The net force is the vector sum of all external forces acting on a chosen object or system: $\vec F_{\text{net}}=\sum\vec F$.

What does a free-body diagram represent?

A free-body diagram shows every external force acting on one selected object. It should not show motion, velocity, or acceleration as forces.

What does Newton’s first law predict when $\vec F_{\text{net}}=0$?

Newton’s first law states that zero net force produces zero acceleration, so an object remains at rest or moves with constant velocity.

State Newton’s second law.

Newton’s second law relates net force, mass, and acceleration: $\vec F_{\text{net}}=m\vec a$. In components, $\sum F_x=ma_x$ and $\sum F_y=ma_y$.

What distinguishes a Newton’s third-law force pair?

A third-law pair consists of equal-magnitude, opposite-direction forces of the same interaction acting on different objects.

How do mass and weight differ?

Mass is an intrinsic property measured in kilograms. Weight is the gravitational force on an object, measured in newtons, and near Earth has magnitude $w=mg$.

What is the normal force on a frictionless incline?

The normal force is perpendicular to the surface. On an incline with no perpendicular acceleration, its magnitude is $N=mg\cos\theta$.

What is tension, and where does it act?

Tension is a pulling force transmitted along a stretched rope, cable, or string. For an accelerating hanging mass, $T-mg=ma_y$.

What does Hooke’s law describe?

An ideal spring follows Hooke’s law: $\vec F_s=-k\vec x$. The negative sign means the spring force points opposite the displacement from equilibrium.

How is static friction modeled?

Static friction adjusts as needed up to its maximum: $0\le f_s\le\mu_sN$. It equals $\mu_sN$ only at the threshold of slipping.

What is the model for kinetic friction?

Kinetic friction acts while surfaces slide and is modeled by $f_k=\mu_kN$. It opposes relative slipping at the contact surface.

What is a block’s acceleration down a frictionless incline?

For a frictionless incline, the component of gravity parallel to the slope gives $mg\sin\theta=ma_{\parallel}$, so $a_{\parallel}=g\sin\theta$.