Physical Science: Chapter 10 - Study Guide

Force

Push or a pull

What is force described by?

Its magnitude and by the direction in which it acts

SI unit of force

Newton

Net force

The combination of all forces acting on an object

When 2 or more forces act in the same direction

Add strengths of the individual forces. The net force acts in the same direction of the individuals forces.

When 2 or more forces act in opposite directions

Add the strengths of the individuals forces (Adding a positive number to a negative number). The net force acts in the direction of the greater force.

Equal but opposite forces

No net force

What do unbalanced forces result in?

A net force and a change in the object’s velocity

Balanced forces

Equal forces acting on one object in opposite directions

What do balanced forces result in?

No net force and no change in the object’s velocity

Friction

A force that two surfaces exert on each other when they rub against each other

What does the strength of the force of friction depend on?

The types of surfaces involved and on how hard the surfaces push together

Do smooth surfaces or rough surfaces produce less friction?

Smooth surfaces

Do surfaces pushing hardly or lightly against each other produce more friction?

Hardly

Static friction

The friction that acts on objects that are not moving

Sliding friction

When 2 solid surfaces slide over each other

Rolling friction

When an object rolls across a surface

Fluid friction

When a solid object moves through a liquid

Gravity

A force that pulls objects toward each other

The Universal Law of Gravitation

The force of gravity acts between all objects in the universe

The force of gravity between objects increases with what and decreases with what?

Increases with greater mass and decreases with greater distance

Mass

The amount of matter in an object

SI unit of mass

Kilogram

Weight

The gravitational force exerted on a person or object at the surface of a planet

Formula for weight

Weight = Mass x Acceleration due to gravity (Earth: 9.8 m/s²)

SI unit of weight

Newton/kg x m/s²

Free Fall

When the only force acting on an object is gravity

In free fall, the force of gravity causes what

An object to accelerate in the downward direction

All objects in free fall accelerate at the same rate of what regardless of their masses?

9.8 m/s²

Air resistance

An upward force exerted on falling objects

Do objects with a greater or smaller surface area experience more air resistance as they fall?

Greater

When is matter considered elastic?

If it returns to its original shape after it is squeezed or stretched

Compression

An elastic force that squeezes or pushes matter together

Tension

An elastic force that stretches or pulls matter

Newton’s first law of motion (law of inertia)

An object will remain at rest or moving at a constant velocity unless it is acted upon by an unbalanced force

Inertia

The tendency of an object to resist a change in motion

The greater the mass of an object is…(inertia)

The greater its inertia, and the greater the force required to change its motion

How do you increase acceleration?

An increase in force and a decrease in mass

How do you decrease acceleration?

A decrease in force and an increase in mass

Newton’s second law of motion

Acceleration depends on the net force acting on the object and on the object’s mass

Formula for acceleration

Acceleration = Net force/Mass

Newton’s third law of motion

If 1 object exerts a force on another object, then the second object exerts a force of equal strength in the opposite direction on the first object

Why can’t you detect all motion when paired forces are in action?

Earth’s inertia is so great due to its mass that its acceleration is too small to notice

Why don’t the action and reaction forces in Newton’s third law of motion cancel out like balanced forces?

The action and reaction forces act on different objects

Momentum (“a quantity of motion”)

A characteristic of a moving object that depends on both the mass and velocity of the object

Formula for momentum

Momentum = Mass x Velocity

SI unit of momentum

Kilogram-meters per second (Kg x m/s)

Is momentum a vector?

Yes

The momentum of an object is the same direction as what?

Its velocity

The more momentum a moving object has, the harder it is to what?

Change its velocity

Greater what and greater what results in more momentum?

Greater mass and greater velocity

Law of conservation of momentum

The total momentum of any group of objects remains the same, or is conserved, unless outside forces act on the objects

How do rockets and space shuttles lift into space?

Using Newton’s third law of motion (The gases it expels with a downward action force exerts an equal but opposite reaction force on the rocket)

What causes a change in the rocket’s velocity?

The upward force called thrust is greater than the downward force of gravity, resulting in an unbalanced force

Satellite

Any object that orbits another object in space

Artificial Satellite

A device that is launched into orbit

Centripetal Force

Any force that causes an object to move in a circular path

If an object is accelerating, what does that mean?

An unbalanced force is acting on it

What happens at a certain speed?

The path of the object would match the curve of the Earth, so Earth’s surface would curve away from the ball at the same rate

What happens to a satellite above the equator because Earth rotates once every 24 hours?

It always stays at the same point above Earth as it rotates