Physics midterm 2

Topics 5 -7 ( Dynamics, Energy and Linear Momentum)

Forces are a measure of….

the interaction between objects

Inertia

opposing the change of motion

Net force

The vector sum of all forces applied to an opject

Newtons first law

selecting a set of inertia reference frames, that are observed from a body that is at rest or has constant velocity (no acceleration), no net force is acting on it.

If still means no force pushing

Newtons second law

The net force acting on a body is equal to the mass x the acceleration

Fnet = ma

Newtons third law

Body A exerts a force on body B. Body B also exerts an equal force in opposite direction on body A

F b on a = -F a on b

you push on something and it pushes back

Does force cause motion?

No, force causes acceleration or change in the state of motion.

Same reason we don’t count forces that are no longer touching the body in question

If an object is thrown as a projectile (e.g at an angle with the horizontal), does the “force of the throw” pushing it forward?

No, the object is no longer touching your hand so the force no longer counts. Force causes change in the state of motion not the motion itself

Force of gravity

Fg = mg

gravity is dependant on the mass of the object, its greater for the larger mass of the object

what is weight?

weight is gravities affect on mass

What is a reaction force

forces that arise in connection with some other interaction. Cuased by another force or other external condition

Normal force

force between 2 objects that are pushing on each other. Always perpendicular. Think newtons third law. You push on something and it pushes back

Friction

irregularies in the forces being contacted. 2 types of friction, kinetic and static.

kinetic friction is when

occurs when the object is moving

static friction is when

occurs when the object is static or not moving

Air resistance

the frictional force exerted by the air on a moving object

Tension

force inside a rope. Force by which a rope will pull on an object

Steps for drawing free body diagram

1. identify all the might exert a force on object

2. Identify newtons third law pairs (Fn)

3. Identify coordinates, F net = 0 and acceleration

4 basic forces

1. Gravitational

2. Electromagnetic

3. Stong (nuclear)

4. Weak

Conservation of energy

The total energy of a system is conserved

Work

Change in energy.

Break down the work equation

When the force acting on the object is constant and the direction doesn’t change. W = |F| x d x cos

W = Force acting on the object x distance along where the force is acting x Cos of the angle between the direction of force and motion

work in same direction

positive work

work in opposite direction

negative work

work in perpendicular motion

zero work

Net work can be calculated in 2 ways

• work done by the net force (all together)

• sum of the work done by each force (individual)

Break down Hookes law

F = -kx

k(spring constant) x(distance from spring equilibrium. When the spring is still then the distance to where it is currently stretched)

Work is negative/positive when k is

+k= negative work

-k= positive work

decreasing/increasing potential energy when the work is

Increasing potential energy = negative work

Decreasing potential energy = positive work

When is the total energy for the system constant

no dissipative forces like air resistance

What is Wnet equal to

change in the objects kinetic energy

what is the change in the total mechanical energy equal to

amount of work done by non -conservative forces

What does it mean for the total energy is the system is isolated

The total energy is always conserved

Power

The rate at which work is done or energy is transferred

heisenburg principle (search)???