Warm-up or stretching first?

Recently,my friend asked me whether to perform warming up first or stretching before running.I then found out that most of my friends perform stretching without any warming up before running.Is it a hassle to perform warming up?
This are what i find out....

1)What is Warm-up?

Warm-up involves warming up and preparing specific muscles and the body for the extra stress of strenuous physical activity.The warm up basically has 3 components,namely consists of;

-the WARM UP consisting of low intensity rhythmic activities to increase muscle and body temperature

-the STRETCH to lengthen muscle and tendon tissue and to increase range of joint movement

-the SPECIFIC SPORT that you are performing

2)Why we need to Warm-up?

The warm up is an essential part of any competition and activity session.
An effective warm up:

-prepares the muscles,tendons and joints for the movement required during exercises
-increases flexibility
-allows the muscles to contract more effectively and coordinate better
-increases body temperature
-increases blood and oxygen supply to the working muscles

Thus,warming up will assist in reducing the risk of getting injure and increase the level of performance.

3)When to do a Warm-up?

-the environment conditions

The environmental conditions play an important role in the structure and duration of the warm up.If the outside temp is low,duration of warm up will need to be longer and if the outside temp is hot,warm up of shorter period is adequate.

-Intensity

The intensity of the warm up should be such that the participants are able to hold a conversation.They should start slowly,exercising well within their capabilities,and gradually build up the intensity.Participants should be able to fell an increase in heart beat and breathing rate during a warm up.

-Duration

The duration of warm up will depends on the environment.A 5 to 10 minutes warm up is generally sufficient.

4)How to Warm-up?

-The type of activity used should not be strenuous,difficult to perform,require fine motor coordination and long periods of static activity.

-The suitable warm up are jogging,brisk walking,slow swim or slow cycle.

Warming up alway precedes stretching.So next time be sure that you perform a warm up activity before stretching......

Refer to this link for specific running warm up from runner's world.