bodyApplyGravity(body) {
		// apply gravity to the current velocity
		if (!body.ignoreGravity && body.gravityScale !== 0) {
			const gravity = this.gravity;

			// apply gravity if defined
			body.force.x += body.mass * gravity.x * body.gravityScale;
			body.force.y += body.mass * gravity.y * body.gravityScale;
		}
	}
Apply gravity to the given body
@private
@param {Body} body