The Laws of Motion

Question and answer review flashcards based on lecture notes covering forces, gravity, friction, Newton's three laws of motion, momentum, and collisions.

What is a contact force?

A push or pull on one object by another that is touching it.

What is a noncontact force?

The force one object can apply to another without touching it.

How do mass and gravity differ?

Mass is the amount of matter in an object, whereas gravity is the attractive force between all objects that have mass.

What does the law of universal gravitation state?

All objects are attracted to each other by a gravitational force.

What is the relationship between gravitational force and distance?

The gravitational force between objects decreases as the distance between the objects increases.

What is friction?

A force that resists the motion of two surfaces that are touching.

What are the definitions of static friction, sliding friction, and fluid friction?

Static friction prevents two surfaces from sliding past each other; sliding friction opposes the motion of objects sliding past each other; fluid friction occurs between a surface and a material that flows.

What are two reasons friction occurs between surfaces?

1. Microscopic dips and bumps on one surface catch on those of another surface when they slide past each other. 2. Attraction between electrical charges in surface particles slows their sliding past each other.

How do lubricants reduce friction?

Lubricants decrease friction by slightly separating surfaces as they slide past each other.

What is Newton's first law of motion?

If the net force on an object is zero, an object at rest will stay at rest, and an object in motion will continue moving in a straight line with a constant speed.

What is inertia?

Inertia is the tendency of an object to resist a change in its motion.

How do balanced and unbalanced forces affect an object's velocity?

Balanced forces acting on an object result in an unchanged velocity, while unbalanced forces acting on an object result in a changed velocity.

What is the difference between velocity and acceleration?

Velocity is the speed and direction in which an object is moving, while acceleration is a change in velocity.

What is Newton's second law of motion?

The acceleration of an object is equal to the net force exerted on the object divided by the object's mass.

In Newton's second law equation $a = F/m$, what do the variables represent and what are their units?

$a$ stands for acceleration (in $\text{m/s}^2$), $F$ stands for net force (in $\text{N}$), and $m$ stands for mass (in $\text{kg}$).

What is Newton's third law of motion?

When one object applies a force on a second object, the second object applies a force of the same size but in the opposite direction on the first object.

What is a force pair?

The forces two objects apply on each other, consisting of an action force and a reaction force of equal size and opposite direction.

Why do force pairs not cancel each other out to produce a net force of zero?

Combining forces results in a net force of zero only if the forces act on the same object, whereas force pairs act on two different objects.

What is momentum?

The measure of how hard it is to stop a moving object.

In the momentum equation $p = m \times v$, what do the variables represent and what are their units?

$p$ stands for momentum (in $\text{kg}\times\text{m/s}$), $m$ stands for mass (in $\text{kg}$), and $v$ stands for velocity (in $\text{m/s}$).

Which object has greater momentum: a $10\text{ kg}$ shopping cart moving at $5\text{ m/s}$ or a $2\text{ kg}$ ball moving at $28\text{ m/s}$?

The $2\text{ kg}$ ball moving at $28\text{ m/s}$ has a momentum of $56\text{ kg}\times\text{m/s}$, which is greater than the shopping cart's momentum of $50\text{ kg}\times\text{m/s}$.

What is the law of conservation of momentum?

The total momentum of a group of objects stays the same unless outside forces act on the objects.

How do elastic and inelastic collisions differ?

In elastic collisions, objects bounce off each other, whereas in inelastic collisions, objects stick together. Momentum is conserved in both types.