Newton's Laws

The force or component of a force which a surface exerts on an object with which it is in contact, and which is perpendicular to the surface.

The force that opposes the motion of an object and which acts parallel to the surface.

The force that opposes the tendency of motion of a stationary object relative to a surface.

The force that opposes the motion of a moving object relative to the surface.

A body will remain in its state of rest or motion at constant velocity unless a non-zero resultant/net force acts on it.

When a net force acts on an object, the object will accelerate in the direction of the net force and the acceleration is directly proportional to the force and inversely proportional to the mass of the object.

When object A exerts a force on object B, object B simultaneously exerts an oppositely directed force of equal magnitude on object A.

Each body in the universe attracts every other body with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centres.

The gravitational force the Earth exerts on any object on or near its surface. Measured in Newtons (N). Calculated: w = mg.

The amount of matter in a body. Measured in kilograms (kg). Stays constant regardless of location.

The resistance of a body to change in its state of uniform motion or rest. Newton’s First Law is often called the Law of Inertia.

The sensation experienced when all contact forces are removed (e.g., free fall).

A diagram showing the relative magnitudes and directions of the forces acting on a body/particle that has been isolated from its surroundings. The object is represented by a dot.

Normal force equals the gravitational force (N = mg) when the object is on a horizontal surface and no other vertical forces are acting.

fs(max) = μs * N (μs is coefficient of static friction; N is normal force).

fk = μk * N (μk is coefficient of kinetic friction; N is normal force).

• Proportional to normal force. 2. Independent of the area of contact. 3. Independent of the velocity of motion.

If applied force does not move object, F = f_s. Static friction reaches a maximum (f_smax) just before object moves. If applied force exceeds f_smax, net force accelerates object, and kinetic friction (f_k) acts.

Fnet = m * a (Net force = mass x acceleration). Direction of acceleration is same as Fnet.

F = (G * m1 * m2) / r² (G = 6.67 x 10^-11 N·m²·kg-²).

g = G * M / r² (M = mass of planet; r = distance from centre of planet).

Acceleration is directly proportional to Fnet; Acceleration is inversely proportional to mass (a = Fnet / m).

• Equal in magnitude. 2. Opposite in direction. 3. Act on different objects. 4. Act simultaneously.

Passengers in a moving car have inertia (they move at same speed as car). When car suddenly stops, passengers continue moving forward. Seatbelts exert force to stop them, preventing injury.