In order to change the motionOf an object, you must apply

A force to it.

A force is the cause of an Acceleration, or the change

In an object’s motion.

The SI unit of force is the Newton,Labeled with an, N.

Force is a VECTOR quantity!

The Newton is a derived unit Named after the famous

Isaac Newton.

It is a derived unit that comesFrom multiplying acceleration

By mass.

1 N = 1kg X 1 m/s2

Forces can act through contactOr at a distance.

Contact forces are forces thatArise from the physical Contact of two objects.

Field forces are forces thatAct across a distance, not

Through contact.(i.e. magnets or gravity)

In order to show forces on paper,We use force diagrams.

A force diagram is a diagram ofThe objects involved in a situation

And the forces exerted on The objects.

Another way of showing theForces involved on an object

Is a free body diagram.

It is basically a force diagramThat has only an isolated object.

An object at rest remains at rest, And an object in motion continuesIn motion with constant velocity

(that is, constant speed in a Straight line) unless it experiences

A net external force.

The tendency of an object not To accelerate is called inertia.

The net external force is the Total force resulting from a

Combination of external forcesOn an object; sometimes

Called the resultant force.

Inertia is directly related to The mass of the object.

The greater the mass, the lessThe object will accelerate under

A given force.

Equilibrium is the state of a Body in which there is no

Change in its motion.

The acceleration of an object is Directly proportional to the net

External force acting on the Object and inversely proportional

To the mass of the object.

This is much easier to write As an equation…

F = ma

FORCE SYMBOL Definition Direction

Friction Ff The contact force that acts to oppose sliding motion

opposite the direction of sliding

Normal FN The contact force exerted by a surface on an object

Perpendicular to the surface

Spring Fsp The pull or push a spring exerts on an object

Opposite the object at end of spring

Tension Ft The pull exerted by a string or rope when attached to a body

Away from object and along string

Thrust Fthrust A general term for the forces that move rockets

or planes

Same direction of acceleration

Weight Fg A long-range force due to gravity between objects

Straight down to the center of earth

The normal force is a contact Force exerted by one object on

Another in a direction Perpendicular to the surface

Of contact.

The normal force is alwaysPerpendicular to the surface, Not necessarily opposite the

Force of gravity.

F = ma

The weight of an object isThe magnitude of the force

Of gravity acting on that object.

w = mg

A 5.5 kg watermelon is pushed Across the table. If the

Acceleration of the watermelon Is 4.2 m/s2 to the right, find

The net external force.

F = 23 N to the right

A ball is pushed off with a force Of 13.5 N accelerates at

6.5 m/s2 to the right. What isThe mass of the ball?

2.1 kg

The constant velocity that is Reached when the drag force Equals the force of gravity is Called the Terminal Velocity.

The terminal velocity of a personOut stretched is about

60 m/s!

An interaction pair is a Pair of simultaneous equal but

Opposite forces resulting from theInteraction of two objects.

If two bodies interact, the Magnitude of the force exerted On object 1 by object 2 is equalTo the magnitude of the force

Simultaneously exerted on object2 by object 1, and these two forces

Are opposite in direction.

This is better stated as For every action, there is an Equal by opposite reaction.

When a softball with a mass of 0.18 kg is dropped, its acceleration

Is g. What is the force on the Earth due to the ball, and what is

Earth’s acceleration? Earth’s mass is 6.0 X 1024 kg

1.8 N 1.8 N 2.9 X 10-25 m/s

A 50 kg bucket is being lifted by a Rope. The rope will not break if the Tension is 525 N or less. The bucket

Started at rest, and after being lifted 3 m, it is moving at 3 m/s. If the Acceleration is constant, is the

Rope in danger of breaking?

570 N, yes it will break!

There are only 4 fundamental Forces of nature…

Gravitational Forces

Electromagnetic Forces

The Strong Nuclear Force

The Weak Nuclear Force