En el siguiente WEBCAST se ve el compendio de los temas tratados hasta el momento, Clases, Objetos en aplicaciones Silverlight.

Código de la clase Balón:

using System;
using System.Net;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Ink;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Animation;
using System.Windows.Shapes;

namespace Silverlight_CPOO_01_Clases_Demo
{
    public class Balon
    {
        private const double distancia = 10;
        public Ellipse Grafico { get; set; }

        public Balon()
        {
            Grafico = new Ellipse();
            Grafico.Height = 50;
            Grafico.Width = 50;
            Grafico.Fill = new SolidColorBrush(Colors.Green);
        }

        public void MoverArriba()
        {
            double posTop = (double)Grafico.GetValue(Canvas.TopProperty);
            posTop -= distancia;
            Grafico.SetValue(Canvas.TopProperty, posTop);
        }

        public void MoverAbajo()
        {
            double posTop = (double)Grafico.GetValue(Canvas.TopProperty);
            posTop += distancia;
            Grafico.SetValue(Canvas.TopProperty, posTop);
        }

        public void MoverIzquierda()
        {
            double posLeft = (double)Grafico.GetValue(Canvas.LeftProperty);
            posLeft -= distancia;
            Grafico.SetValue(Canvas.LeftProperty, posLeft);
        }

        public void MoverDerecha()
        {
            double posLeft = (double)Grafico.GetValue(Canvas.LeftProperty);
            posLeft += distancia;
            Grafico.SetValue(Canvas.LeftProperty, posLeft);
        }
    }
}

Código de la clase MainPage

using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Animation;
using System.Windows.Shapes;

namespace Silverlight_CPOO_01_Clases_Demo
{
    public partial class MainPage : UserControl
    {
        Balon balon;
        public MainPage()
        {
            InitializeComponent();
            Loaded += new RoutedEventHandler(MainPage_Loaded);
        }

        void MainPage_Loaded(object sender, RoutedEventArgs e)
        {
            balon = new Balon();
            LayoutRoot.Children.Add(balon.Grafico);
        }

        private void btArr_Click(object sender, RoutedEventArgs e)
        {
            balon.MoverArriba();
        }

        private void btIzq_Click(object sender, RoutedEventArgs e)
        {
            balon.MoverIzquierda();
        }

        private void btAba_Click(object sender, RoutedEventArgs e)
        {
            balon.MoverAbajo();
        }

        private void btDer_Click(object sender, RoutedEventArgs e)
        {
            balon.MoverDerecha();
        }
    }
}

Código de la UI para el manejo del Balón:

<UserControl x:Class="Silverlight_CPOO_01_Clases_Demo.MainPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d"
    d:DesignHeight="300" d:DesignWidth="400">

    <Canvas x:Name="LayoutRoot" Background="White">
        <Button Canvas.Left="244" Canvas.Top="227" Content="Arriba" Height="23" Name="btArr" Width="75" Click="btArr_Click" />
        <Button Canvas.Left="163" Canvas.Top="256" Content="Izquierda" Height="23" Name="btIzq" Width="75" Click="btIzq_Click" />
        <Button Canvas.Left="244" Canvas.Top="256" Content="Abajo" Height="23" Name="btAba" Width="75" Click="btAba_Click" />
        <Button Canvas.Left="325" Canvas.Top="256" Content="Derecha" Height="23" Name="btDer" Width="75" Click="btDer_Click" />
    </Canvas>
</UserControl>