With this sketch your Arduino can detect acceleration using an analog accelerometer

analog_acceleration.ino

int x, y, z;

void setup()
{
	Serial.begin(9600); // sets the serial port to 9600
}

void loop()
{
	x = analogRead(0); // read analog input pin 0
	y = analogRead(1); // read analog input pin 1
	z = analogRead(2); // read analog input pin 1
	Serial.print("accelerations are x, y, z: ");
	Serial.print(x, DEC); // print acceleration in the X axis
	Serial.print(" "); // prints a space between the numbers
	Serial.print(y, DEC); // print acceleration in the Y axis
	Serial.print(" "); // prints a space between the numbers
	Serial.println(z, DEC); // print acceleration in the Z axis
	delay(100); // wait 100ms for next reading  
}