Initialize force and angle base on sliders.

src/main/java/lab/GameController.java

 package lab;
 
 import javafx.animation.AnimationTimer;
-import javafx.beans.value.ChangeListener;
-import javafx.beans.value.ObservableValue;
 import javafx.fxml.FXML;
 import javafx.scene.canvas.Canvas;
 import javafx.scene.control.Slider;
@@ -27,7 +25,9 @@ public class GameController {
 	public void startGame() {
 		this.world = new World(canvas.getWidth(), canvas.getHeight());
 		angleSlider.valueProperty().addListener( (val, oldValue, newValue) -> world.setAngle(newValue.doubleValue()));
+		world.setAngle(angleSlider.getValue());
 		forceSlider.valueProperty().addListener( (val, oldValue, newValue) -> world.setForce(newValue.doubleValue()));
+		world.setForce(forceSlider.getValue());
 		//Draw scene on a separate thread to avoid blocking UI.
 		animationTimer = new DrawingThread(canvas, world);
 		animationTimer.start();