Need help with my frictional physics

onClipEvent (load) {
	// initialize variables
	fcount = 0;
	x_momentum = 0;
	y_momentum = 0;

	// trigonometric function for movement 
	function move (distance) {
		angle = (_rotation/360)*2*Math.PI;
		x_momentum += distance*Math.sin(angle);
		y_momentum += -distance*Math.cos(angle);
	}
}
onClipEvent (enterFrame) {
	// increment frame counter
	fcount++;

	// keypress detection
	if (Key.isDown(Key.UP)) {
		move(1);
	}
	if (Key.isDown(Key.DOWN)) {
		move(-1);
	}
	if (Key.isDown(Key.LEFT)) {
		_rotation -= 5;
	}
	if (Key.isDown(Key.RIGHT)) {
		_rotation += 5;
	}

	// movement due to momentum
	_x += x_momentum;
	_y += y_momentum;

	// set borders to bounce
	if (_y<20 or _y>380) {
                // undo y-momentum from y-postion
		_y -= y_momentum;
                // reverse y-momentum
		y_momentum *= -1;
	}
	if (_x<20 or _x>480) {
                // undo x-momentum from x-postion
		_x -= x_momentum;
                // reverse x-momentum
		x_momentum *= -1;
	}

	// apply friction when frame count is max (every 10th frame)
	if (fcount >=10) {
		// x-component friction:
		// if x-momentum is positive, decrease it by a 0.01
		if (x_momentum>0) {
			x_momentum -= 0.01;
			// if the x-momentum is "small", make it equal zero
			if (x_momentum<0.001) {
				x_momentum = 0;
			}
		// if x-momentum is negative, increase it by a 0.01
		} else if (x_momentum<0) {
			// if the x-momentum is "small", make it equal zero
			x_momentum += 0.01;
			if (x_momentum<0.001) {
				x_momentum = 0;
			}
		}

		// y-component friction:
		// if y-momentum is positive, decrease it by a 0.01
		if (y_momentum>0) {
			y_momentum -= 0.01;
			// if the y-momentum is "small", make it equal zero
			if (y_momentum<0.001) {
				y_momentum = 0;
			}
		// if y-momentum is negative, increase it by a 0.01
		} else if (y_momentum<0) {
			y_momentum += 0.01;
			// if the y-momentum is "small", make it equal zero
			if (y_momentum<0.001) {
				y_momentum = 0;
			}
		}
	}

	// reset the frame count when max is reaches
	if (fcount >=10) {
		fcount = 0;
	}
}