An internal combustion engine usable for producing a rotational output, the internal combustion engine comprising: a casing; a cylinder defining a cylinder head and a combustion chamber extending from the cylinder head, the combustion chamber being substantially arc segment shaped and defining a chamber radius of curvature, the cylinder being mounted to the casing so as to be movable relatively thereto along a substantially annular path extending in a substantially concentric relationship relatively to the combustion chamber, the substantially annular path having a path radius of curvature substantially similar to the chamber radius of curvature; a piston, the piston being operatively coupled to the cylinder so as to be reciprocatingly movable within the combustion chamber, the piston being mounted to the casing so as to be movable relatively thereto along the substantially annular path; an output element operatively coupled to the cylinder and to the piston for producing the rotational output; and a unidirectional coupler operatively coupling at least one of the cylinder and the piston to the casing such that the at least one of the cylinder and the piston is unidirectionally movable relatively to the casing.