Forces and Motion PS9.21 PS9.22 PS9.23 PS9.24 ps9.25

Forces can create changes in motion 3 types of acceleration (change in speed or direction (acceleration) speeding up Deceleration is negative acceleration or slowing down Centripetal acceleration changing direction

Motion can be described as a change in an object’s position Average velocity (speed) is the change of position of an object over time

Velocity Graphs V = distance time Velocity (v) is the slope (rise over run) of a position (d) vs. time (t) graph

40 The diagram represents the total travel of a teacher on a Saturday 40 The diagram represents the total travel of a teacher on a Saturday. Which part of the trip is made at the greatest average speed? F Q G R H S J T How do we work this one? Calculate v = d/t for each segment.

Acceleration Graphs Acceleration (a) is the slope of a velocity (v) vs. time (t) graph Plotted on a distance vs. time graph, acceleration is an exponential curve

Acceleration is a change in an objects velocity (speed or direction) When an object’s speed changes over time it is accelerating (or decelerating) A = vfinal – vinitial time Units for acceleration m/s/s or m/s2

Definition of a Force A Force is a push or a pull

Balanced Force A force that produces no change in an object’s motion because it is balanced by an equal, opposite force. If you were to add these forces they would = 0

Unbalanced Forces Are forces that results in an object’s motion being changed. + Add together to equal greater force.

Friction A force that acts in a direction opposite to the motion of two surfaces in contact with each other.

Friction Friction causes an object to slow down and stop. Since the amount of energy stays constant, the energy becomes heat. Air resistance is an another example of friction. Lubricants or grease reduce friction.

Newton’s 1st Law of Motion Object in motion stays in motion

Newton’s 1st Law of Motion And Objects at rest stay at rest

Newton’s 1st Law of Motion Until they are acted upon by unbalanced forces.

Inertia or Newtons 1st Law Tendency for an object to stay at rest or moving in a straight line at a constant speed. The mass (m measured in kg) of an object determines its inertia Inertia comes from the Latin word meaning lazy.

Newton’s 2nd Law of Motion Force = Mass X Acceleration F=ma Weight (pull of gravity) is a commonly measured force, calculated by F=mg, g is the acceleration due to gravity 9.8 m/s2

Newton’s 2nd Law of Motion The greater the mass of an object, the greater the force required to change its motion.

Newton’s 2nd Law of Motion The greater the acceleration of an object, the greater the force required to change its motion.

Formula chart says F=ma, m is mass in kg, a is acceleration in m/s2. 11 The frog leaps from its resting position at the lake’s bank onto a lily pad. If the frog has a mass of 0.5 kg and the acceleration of the leap is 3 m/s2, what is the force the frog exerts on the lake’s bank when leaping? A 0.2 N B 0.8 N C 1.5 N D 6.0 N Formula chart says F=ma, m is mass in kg, a is acceleration in m/s2. So, .5 kg x 3 m/s2= 1.5 N

Newton’s 3rd Law of Motion For every action force there is an equal and opposite reaction force.

Newton’s 3rd Law of Motion All forces come in action-reaction pairs Ex: feet push backward on floor, the floor pushes forward on feet

Universal Law of Gravitation Between any two objects in space there is gravity

Universal Law of Gravitation Gravity varies depending on two factors: 1) the mass of the object doing the pulling, and 2) the distance from the center of that object

On Earth gravity = 9.8 m/s/s For every second that an object falls its speed increases by 9.8 m/s