FORCE, SPEED, AND ACCELERATION

Force- an action that has the ability to change motion (push, pull) Units- pounds or Newtons

1N = 1kg x 1 m/sec2

Mass- the amount of matter in an object Units- grams or kilograms Mass is the same everywhere

Weight- the amount of mass with gravitational pull Units- pounds or Newton Weight changes due to gravity

Motion-a change in position. Position- where something is

compared with where it started, including direction Ex. 7km North of Building A

Distance-interval of length without regarding direction Ex. I walked 14km

An object at rest is a special case of motion in which there is not change in position

How can the motion of an object be changed? Change how fast it is moving

Starting Stopping Changing speeds

Change its direction

How does graphing fit in?(It’s never going to go away!)

Position vs. Time graphs show where things are at a different times which makes it easy to see how things have moved.

EX:

Moving Away Moving to StartStopped

Newton’s 1st Law- law of inertia An object at rest will stay at rest and an

object in motion will stay in motion unless an unbalanced force is acted upon it.

Inertia- the property of an object to resist changing its state of motion.

The amount of inertia an object has depends on its mass.

Newton’s 2nd Law The acceleration of an object is directly

proportional to the force acting on it and inversely proportional to its mass. Force causes acceleration Mass resists acceleration The acceleration you get is equal to the

ratio of force over mass a=F F=ma m

Force isn’t necessary to keep an object in motion at constant speed.

The motion of an object depends on the total of all forces acting on the object- net force.

When forces on an object are balanced, the net force is zero=equilibrium.

Acceleration- the rate at which something speeds up or slows down

Formula: a=Vf-Vi/t

How does speed fit in?

Speed-the distance an object travels divided by the time it takes Speed is the rate of motion

Rate-ratio between two different quantities (distance/time)

Units: m/s or km/hr Formula: V=d/t

speed=distance/time Constant speed-the speed does not

change Instantaneous speed- the speed at a

single instant of time

Graphing…another connection! Distance vs. Time graphs show how

speed changes at different places.

TIme

Distance

Velocity- the speed and direction of the object. The velocity of an object is the rate at

which its position changes over time and the direction of the change. Ex:

Speed= 220 km per hour Velocity= 220 km per hour due north

Velocity can change even if speed remains constant (because you could change direction)

Gravity- a force that pulls every mass toward every other mass. Gravity depends on how much mass, Gravity= 9.8 N or 9.8 m/sec2

Law of Universal Gravitation- gravity is a force of attraction that exists between any two objects that have mass. Force of attraction increase when mass

increases. Force also increases when objects get

closer.

Calculating force between two objects

G= Gravitational constant 6.67x1011 N·

m2/kg2

221

R

mmG F

221

d

mm*G F

Weight- force created by gravity on an object. Depends on the objects mass

Calculating Fw= mg (9.8 m/sec2) W= mg

Units- N or lbs NOT kg

Friction- forces that result from relative motion between objects. Friction forces always work against the

motion that produces them. Friction is opposite whatever force is

causing it. Wear- how moving parts can erode

each other Net Force- what is left after

subtracting friction force from gravity. (total force) Friction reduces acceleration All machines have friction

4 types of Friction

Air Friction- air moving around moving objects creates an opposing force.

Sliding Friction- two surfaces rub against each other.

Viscous Friction- objects that move in water or other fluids, oil changes sliding friction to viscous friction.

Rolling Friction- one object rolling over another, like wheel rolling over a road.

Newton’s Third Law That for every action there is an equal and

opposite reaction force. The reaction force is equal in magnitude

and opposite in direction All forces come in pairs The action/reaction forces act on separate

objects not the same object

Momentum- the mass of an object multiplied by its speed or velocity Increase mass or

speed, you increase its momentum

Units Kg*m/sec

mvP momentum

mass

Velocity

Law of Conservation of Momentum- if interaction objects are not influenced by outside forces (friction), the total amount of momentum cannot change. The momentum gained by one body in an

interaction is equal to the momentum lost by the other body.

That means momentum can also be positive (moving to the right) or negative (moving to the left).

Momentum before collision= momentum

after collision

22112211 vmvmvmvm Momentum before Momentum After

Mass Velocity