Chapter 2

ForceForce- push or pull

exerted by one body onto another

Not all forces are easily recognized

Right now several forces are acting on all of us.

Balanced forcesBalanced forces –

equal forces act on an object – and cancel each other out

If the upthrust (or push up) of the air is equal to the force of gravity (pull down), then the balloon remains suspended in the air.

Net ForceNet force – when

one force is greater then another. This is an unbalanced force- and causes an object to accelerate

There may be many force directions in any one movement

NewtonNewton’s first law of motion: An object at

rest tends to stay at rest and an object in motion tends to stay in motion with the same speed and in the same direction unless acted upon by an unbalanced force

ForceForce is equal to the

mass of the object times the objects acceleration. If any two of these are known the third can be found.

F = m x aMass- kilogramsa = m/s2

F = Newtons

InertiaInertia = the

resistance an object has to a change in its state of motion – objects with greater mass have greater inertia

Force is not needed to keep an object in motion.

Forces accelerate or decelerate objects

FrictionFriction- force that

opposes movement between two surfaces that are touching

Causes of friction – unsmooth surface, deformations, molecular attraction

QuestionImagine a place in the cosmos far from all

gravitational and frictional influences. Suppose that you visit that place (just suppose) and throw a rock. The rock will

a. gradually stop. b. continue in motion in the same direction at

constant speed.

GravityGravity is a force that

all matter has on all other matter.

Gravity is affected by mass and distance-

As mass increases gravitation increases

As distance from the mass increases gravitation decreases

Newton’s Law of Gravitation

↑ Einstein’s Theory of General Relativity

Gravity MathNear the surface of the

Earth gravity accelerates objects at 9.8m/s2

Weight is the force of gravity acting on your body

Find weight (Newtons) by multiplying your mass (kg) by acceleration (9.8m/s2)

Your mass is the amount of matter in your body. It does not change based on location.

Your weight can change depending on the gravitation of your location. i.e. the moon