Law of action-reaction. Illustration of a space shuttle launch illustrating Newton's third law of motion: for every action there is an equal and opposite reaction. The massive force (action) generated by hot gases firing downwards from the shuttle's engines produces an equal force (reaction) that pushes the shuttle upwards. This force is required to achieve an escape velocity of at least 40,250 kilometres per hour, the speed an object must attain to escape Earth's gravity.