# Optional Practical: Motion of a cart (Algodoo)

### Introduction

In this exercise you will plot graphs of the motion of a cart but first you need to make the cart.

• Open a new scene in Algodoo
• Draw a rectangle and a circle.
• To make the circles identical draw one than clone it by right clicking and selecting “clone”. Before you this you should set the properties of the circle.
• Set the mass by right clicking the circle and selecting "material" then change the mass to 0.002 kg
• The cake slice makes it easy to see the centre, you can make this appear by right clicking the circle, select appearance then tick “draw circle cake”.
• Set the mass of the rectangle to 4 kg.

Why do you have to make the wheels so light?

Move the rectangle near to the ground (This is the horizontal line across the screen) and place the two circles as wheels on the rectangle.

Fasten the wheels by placing axles in the centre of the wheel.

• To make the trolley move give it a velocity by right clicking the rectangle and selecting velocities set the x velocity to 4 ms-1.

• Try running the animation to make sure it works. You can bring the cart back by clicking “undo”.
• To plot graphs of the motion right click the rectangle and select “show plot”. If you click the X and y axis labels you’ll get a long list of options, choose time for x and x velocity for y.
• Run the animation. You will notice that the velocity isn’t constant, this is due to air resistance which can be switched off by clicking to the right of the play button.

• You can control the motion of the cart as the animation is running by opening the velocity window again, try making the velocity + and -.
• To analyse the graph simply place the cursor on the line and you’ll get x and y values, gradient and area.
• To make the cart accelerate place a thruster on the cart. This is done by clicking the thruster tool and placing it where you want. Set the angle and size of the force by moving your mouse about, this is difficult to explain but try and see what happens.

• View the velocity time and displacement time graphs for motion with constant acceleration.
• You can also make the velocity vector visible by clicking visualize >velocity at the bottom of the velocity window.
• Observe the displacement time and velocity time graphs for different initial velocities and forces.

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