Science- Chapter 2

Force

a push or pull

How are forces described?

velocity and strength

Net Force

the overall force on an object after all the forces are added together

What three things can unbalanced forces cause an object to do?

start moving, stop moving, change direction

True/False
Unbalances forces acting on an object will change the object’s motion

True

Balanced Forces

Equal forces acting on one object in opposite directions

True/False
Balanced forces acting on an object will change the object’s motion

False

What has to act on an object in order to make it stay in motion?

Force

True/False
Once an object is in its natural resting place, it cannot move by itself

True

Inertia

the tendency of an object to resist change in its motion

Mass

the amount of matter in an object

What is the SI unit of mass?

kilograms

What does the amount of inertia an object has depend on?

mass

How can mass be defined in terms of inertia?

the greater the mass of an object, the greater its inertia

What is the equation that describes the relationship among quantities of force, mass, and acceleration?

Force= Mass x Acceleration

How does an increase in force affect acceleration?

it causes an increase in acceleration

What are two ways you can increase the acceleration of an object?

– Increase the force used – Change the mass

How does an increase of mass affect acceleration?

it causes a decrease in accleration

True/False
One way to increase the force used to pull a wagon is to decrease the mass in the wagon

True

True/False
When two surfaces rub, the irregularities of one surface get caught on those of the other surface

True

Friction acts in a direction _____ to the object’s direction of motion

opposite

The strength of the force of friction depends on what two factors?

– the types of surfaces involved -how hard the surfaces push together

Fluid Friction

an object moves through fluid

Sliding Friction

solid surfaces slide over each other

Rolling Friction

an object rolls over a surface

Gravity

the force that puuls objects toward each other

When is an object said to be in free fall?

when it is being forced upon by gravity

Near the surface of Earth, what is the acceleration of an object due to the force of gravity?

9.8 m/s squared

Projectile

an object that is thrown

True/False
An object that is dropped will hit the ground before and object that is thrown horizontally

False

Air Resisitence

objects falling through air experience this type of fluid friction

True/False
The greater the surface area of an object, the greater the air resistence

True

Terminal Velocity

the greatest velocity a falling object reaches

Weight

the force of gravity on a person or object at the surface of a planet

How is weight different than mass?

weight is a measure of the force of gravity on an object; mass is a measure of the amount of matter that is in an object

What is weight usually measure in?

Newtons

True/False
The force that makes an apple fall to the ground is the same force that keeps Earth orbiting the sun

True

What does the universal law of gravitation state?

the force of gravity acts between all objects in the universe

True/False
On the moon, your mass would be less than it is on Earth, but your weight would be the same

False

The mass of attraction between two objects varies with what two factors?

mass and square of distance

The law of universal gravitation

the force of gravity acts between all objects in the universe

Newton’s First Law

an object at rest will remain at rest and an object that is moving at a constant velocity will continue moving at constant velocity, unless acted upon by an unbalanced force

Newton’s Second Law

Force= Mass x Acceleration

Newton’s Third Law

if one object exerts a force on another object, then the second object exerts a force of equal magnitude in the opposite direction on the first object

What did Newton call the force exerted by the first object on a second object?

action

What did Newton call the force exerted by the second object back on the first object?

reaction

The action and reaction forces in any situation will always be ____ and ____.

equal opposite

The product of an object’s mass and velocity is its…?

momentum

What is the unit of measurement for momentum?

kilograms x meters per second (kg x mls)

What does the law of conservation of momentum state?

the total momentum of the objects that interact does not change; the quantity of momentum is the same before and after they interact

Friction

the force that one surface exerts o another surface when the two rub against each other