U3T1: GRAVITY AND MOTION

The force of gravity acting on an object.

The force exerted on a body by a surface against which it is pressed. It is always perpendicular (normal) to the surface. For an object at rest on a horizonal surface with no other forces besides gravity, the normal force is equal to the weight force. On an inclined plane with no other forces acting, the normal force equals the perpendicular component of the weight.

Newton's first law of motion states that an object maintains its state of rest or constant velocity motion unless it is acted upon by an external unbalanced force.

<p>Newton's second law of motion states that the acceleration of an object is in the direction of the net external force acting on it and proportional to the size of the force and inversely proportional to mass determined by F=ma.</p> Signup and view all the answers

<p>Newton's third law of motion states that forces always occur in equal and opposite pairs, where for every action force there is an equal and opposite reaction.</p> Signup and view all the answers

<p>Uniform circular motion is the motion of an object travelling at a constant speed in a circle. This is due to a force that acts on this object in a direction that is perpendicular to the velocity of the object.</p> Signup and view all the answers

<p>Centripetal force is the net force directed towards the centre of the circular path. Centripetal acceleration is the acceleration directed towards the centre of the circular path and perpendicular to the velocity vector.</p> Signup and view all the answers

<p>Newton's law of universal gravitation states that the attraction between each pair of point particles is directly proportional to the product of their masses and inversely proportions to the square of the distance between them.</p> Signup and view all the answers

<p>Gravitational field is defined as the region of space surrounding a body in which another body experiences a force of gravitational attraction.</p> Signup and view all the answers

<p>Kepler discovered three laws of planetary motion. The first is the law of orbits, the second is the law of areas and the third is the law of periods.</p> Signup and view all the answers

<p>Kepler's first law of planetary motion states that all planets move about the Sun in elliptical orbits and have the Sun as one of the foci.</p> Signup and view all the answers

<p>Kepler's second law of planetary motion (law of areas) states that a radius vector joining any planet to the Sun sweeps out equal areas in equal lengths of time.</p> Signup and view all the answers

<p>Kepler's third law of motion (law of periods) states that the square of sidereal period of a planet is directly proportional to the cube of the planet's mean distance from the Sun.</p> Signup and view all the answers