AP PHYSICS 1 NEWTON'S LAWS

Newtons first law

An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.

What happens to objects at rest according to Newton's first law?

they will continue in this same state of rest.

What happens to objects that are moving with constant velocity according to Newton's first law?

The state of motion of an object is maintained as long as the object is not acted upon by an unbalanced force. All objects resist changes in their state of motion.

The two conditions of Newton's first law are only true if...

There are ONLY balanced forces. An unbalanced force will cause a change in the state of motion.

Inertia

1. the resistance an object has to a change in its state of motion.

2. tendency of an object to resist changes in its velocity/accerlation

Newton's first law declares...

a force is not needed to keep an object in motion.

What does inertia depend on?

Inertia varies with mass. Mass is that quantity that is solely dependent upon the inertia of an object. The more inertia that an object has, the more mass that it has. A more massive object has a greater tendency to resist changes in its state of motion.

What does it mean when forces are at equilibrium?

Forces are of equal magnitude and in opposite directions, they balance each other.

Unbalanced forces cause...

ACCERLERATION

An object is said to be acted upon by an unbalanced force only when...

there is an individual force that is not being balanced by a force of equal magnitude and in the opposite direction.

Force

push or pull upon an object resulting from the object's interaction with another object. Forces only exist as a result of an interaction.

Types of forces

Contact or action-at-a-distance

Contact forces

when the two interacting objects are perceived to be physically contacting each other. Examples of contact forces include frictional forces, tensional forces, normal forces, air resistance forces, and applied forces.

Action at a distance forces

when the two interacting objects are not in physical contact with each other, yet are able to exert a push or pull despite their physical separation. Examples of action-at-a-distance forces include gravitational forces. Example- planets gravitational pull towards each other and electric forces

Applied force

F app

Force that is applied to an object by a person or another object. If a person is pushing a desk across the room, then The applied force is the force exerted on the desk by the person.

Gravitational force

F grav

The force of gravity is the force with which the earth, moon, or other massively large object attracts another object towards itself. All objects upon earth experience a force of gravity that is directed "downward" towards the center of the earth.

Normal force

F norm

The support force exerted upon an object that is in contact with another stable object.On occasions, a normal force is exerted horizontally between two objects that are in contact with each other. For instance, if a person leans against a wall, the wall pushes horizontally on the person.

Friction force

F frict

The force exerted by a surface as an object moves across it or makes an effort to move across it. Though it is not always the case, the friction force often opposes the motion of an object. For example, if a book slides across the surface of a desk, then the desk exerts a friction force in the opposite direction of its motion.

What causes friction?

the nature of the two surfaces and upon the degree to which they are pressed together.

Air resistance force

F air

A special type of frictional force that acts upon objects as they travel through the air. The force of air resistance is often observed to oppose the motion of an object. This force will frequently be neglected due to its negligible magnitude.It is most noticeable for objects that travel at high speeds (e.g., a skydiver or a downhill skier) or for objects with large surface areas.

Tension force

F tens

The force that is transmitted through a string, rope, cable or wire when it is pulled tight by forces acting from opposite ends. The tension force is directed along the length of the wire and pulls equally on the objects on the opposite ends of the wire.

Mass

The mass of an object refers to the amount of matter that is contained by the object.

What is mass related to?

Mass is related to how much stuff is there and weight is related to the pull of the Earth (or any other planet) upon that stuff. The mass of an object (measured in kg) will be the same no matter where in the universe that object is located.

Weight

The weight of an object is the force of gravity acting upon that object.

What does weight depend on?

Weight depends upon which planet is exerting the force and the distance the object is from the planet. Weight, being equivalent to the force of gravity, is dependent upon the value of g - the gravitational field strength. On earth's surface g is 9.8 N/kg.

The g value is inversely proportional to...

the distance from the center of the planet. So if we were to measure g at a distance of 400 km above the earth's surface, then we would find the g value to be less than 9.8 N/kg.

Solving two body problems

Calculate accerlation then calculate other forces

Newton's third law

For every action force, there is an equal and opposite reaction.

Rule for drawing free body diagrams

Depict all the forces which exist for that object in a given situation

Net force

Vector sum of all the forces which act upon an object

Newton's second law

The acceleration of an object as produced by a net force is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the object.

When free fall occurs, what is the only force acting on it?

Gravity

Object fall at the same rate (9.8) because

Accerlation is dependent on force and mass. Greater mass objects will have greater inertia. The ratio of force to mass is the same for the elephant and mouse in free fall

Air resistance is the result of....

Collisions if the objects leading surface with air molecules

Factors which affect air resistance

Speed of object and cross sectional area of an object

Why does an object that encounters air resistance eventually reach terminal velocity?

As an object falls, it increases speed which increases the amount of air resistance. Eventually, air resistance becomes large enough to balance the force of gravity. At this instant, net force is zero and the object will stop accelerating. The change in velocity terminates as a result of the balance of forces.

Why do more massive objects fall faster than less massive objects?

A more massive object has greater gravitational force and it will accelerate to higher speeds before reaching a terminal velocity.

Static equilibrium

When an object is at rest

If all forces are added together as vectors and there is static equilibrium, theb

The resultant force should equal 0

T/F:Normal force always equals force of gravity

False, if there is an applied force which acts at an angle, then the normal force and the vertical component will equal the force of gravity

Normal force always acts...

Perpendicular to the surface of an object