Forces * Newton’s Laws And Speed

Newton’s Laws First Law - An object at rest tends to stay at rest AND an object in motion tends to stay in motion.

Second Law - The acceleration of an object depends on the net force acting on the object and the object’s mass Third law - When one object exerts a force on a second object, the second object exerts an equal and opposite force on the first.

Motion (or lack of motion) cannot change without an unbalanced force acting.

Balanced forces Tug of war - teams pull in opposite directions If teams pull with the same force, in opposite directions, net force on the rope is ZERO and ---> Rope doesn’t move

Unbalanced forces To move the rope, one team must pull harder than the other.  Net force is NOT zero  Rope will MOVE * Only unbalanced forces cause an object to MOVE (speed up, slow down or change direction).

Average speed is described as a measure of distance divided by time. *Time can be in seconds, minutes, hours *Distance can be meters, kilometers *Speed is a combination of the two: m/s, km/hr Speed = distance or v = d/t time

Distance = speed X time or d = vt Time = distance or t = d/v speed

Velocity and speed are very similar ideas. Velocity is the rate of motion (the speed) in a specific DIRECTION. Example: I'm going that-a-way at 30 kilometers per hour. --> My velocity is 30 kilometers per hour that-a- way.

For velocity you must have both values -> speed and direction. Direction can be described in many ways: *east, west, south, north

When velocity is changing, the word acceleration is used. *You speed up if the acceleration and velocity point in the same direction. * You slow down ( decelerating ) if the acceleration and velocity point in opposite directions.

Momentum is in the same direction as velocity. --> indication of how hard it would be to stop an object. Example --> If you have a tennis ball and a bowling ball both traveling at 3 meters per second, which has greater momentum? Which would be HARDER to STOP? Right! *Right! The bowling ball has a greater momentum, it has more mass.

To calculate momentum: Momentum = mass X velocity

1.A runner finishes a 135 meter race in 24 seconds. What is the runner’s average speed? 2.Find the velocity in meters of a swimmer who swims exactly 110 m toward the shore in 72 s. 3.Find the velocity in meters per second of a baseball thrown 38 m from third base to first base in 1.7 s. 4.Calculate the momentum of a 8 kg bowling ball moving at 12.0 m/s down the alley. 5.An athlete with a mass of 73 kg runs with a constant forward velocity of 1.50m/s. What is their momentum?