Section 1-1 The Nature of Force

Observing Motion by Using a Reference Point Motion- a change in position of an object over time relative to a reference point Reference Point- object that appears to stay in place Common Reference Points Earth Trees Buildings

Speed Speed- the distance traveled by an object divided by the time taken to travel that distance SI unit for speed is m/s Formula for speed Average Speed= total distance/total time Speed is shown on a graph as distance versus time

Velocity: Direction Matters Velocity- speed of an object in a particular direction Difference between speed and velocity is direction Velocity will change either when speed or direction changes Combining Velocity Velocities moving in the same direction are added Velocities moving in opposite directions are subtracted

Acceleration Acceleration- rate at which velocity changes Increase of acceleration- positive acceleration Decrease of acceleration- negative acceleration or deceleration Faster the velocity change, the greater the acceleration Average acceleration= final Velocity – starting velocity/time

Acceleration on a graph Shown on a graph as velocity versus time

Circular Motion: Continuous Acceleration Objects traveling in circular motion are always changing its direction Therefore, velocity is always changing, so it is accelerating Centripetal Acceleration- acceleration that occurs in a circular motion

Force A force is a push or pull All forces have both size and direction The SI unit of force is the newton (N) The more newtons, the greater the force

Forces Act on Objects All forces are exerted by one object on another object One object exerts a force as another receives a force However, just because a force is being exerted by one object on another doesn’t mean that motion will occur

Determining Net Forces Net force- combining all the forces acting on an object Forces in the Same Direction- add the forces together to determine the net force. Forces in Different Directions- subtract the smaller force from the larger force to determine the net force

Unbalanced Forces Produce a Change in Motion When the net force on an object is not zero, the forces on the object are unbalanced Unbalanced forces produce a change in motion Unbalanced forces are necessary to cause a nonmoving object to start moving or change the motion of moving objects An object can continue to move even when the unbalanced forces are removed

Balanced Forces Produce No Change in Motion When the forces applied to an object produce a net force of zero, the forces are balanced Balanced forces do not cause a nonmoving object to start moving Balanced forces will not cause a change in the motion of a moving object