Force and InertiaDynamicsForceNatural MotionIdentifying ForcesFundamental ForcesContact ForcesNewton’s LawsLaw of InertiaInertial Reference FramesForce and InertiaForce and InertiaDynamicsDynamicsKinematics is the study of how things move.Kinematics is the study of how things move.•Position, velocity, and acceleration compared to timePosition, velocity, and acceleration compared to time•Trajectories in spaceTrajectories in spaceDynamics is the study of why things move.Dynamics is the study of why things move.•What causes motion?What causes motion?•How do we use the changes in position and velocity?How do we use the changes in position and velocity?•Force and massForce and massForceForceForce isForce isA push or pull on an object.A push or pull on an object.A vector with magnitude and A vector with magnitude and direction.direction.Force is notForce is notEnergy.Energy.Power.Power.Momentum.Momentum.Velocity.Velocity.Natural MotionNatural MotionA ball is thrown into the air without friction. Before it A ball is thrown into the air without friction. Before it reaches the top it is subject toreaches the top it is subject to•A) a steadily decreasing upward force from the initial toss.A) a steadily decreasing upward force from the initial toss.•B) an increasing downward force of gravity and a steadily B) an increasing downward force of gravity and a steadily decreasing upward force.decreasing upward force.•C) an almost constant downward force of gravity and a C) an almost constant downward force of gravity and a steadily decreasing upward force.steadily decreasing upward force.•D) an almost constant downward force of gravity. D) an almost constant downward force of gravity. •E) a natural tendency to return to the Earth.E) a natural tendency to return to the Earth.Identifying ForcesIdentifying ForcesFind the pushes and pulls on Find the pushes and pulls on the ball in the air.the ball in the air.Isolate the object under Isolate the object under study.study.Look at forces on the object Look at forces on the object alone.alone.handballIn flight, only gravity is pulling on the ball.No force from the hand acts on the ball after release.Fundamental ForcesFundamental ForcesGravity is a fundamental force.Gravity is a fundamental force.It acts upon objects from a distance away from the It acts upon objects from a distance away from the source (such as the Earth).source (such as the Earth).There are two other fundamental forces.There are two other fundamental forces.Electroweak force is Electroweak force is common in everyday life.common in everyday life.•ElectricityElectricity•MagnetismMagnetism•LightLight•Radioactive decayRadioactive decayNuclear force is uncommon Nuclear force is uncommon in everyday life.in everyday life.•Nuclear fission (nuclear Nuclear fission (nuclear power plants)power plants)•Nuclear fusion (stars)Nuclear fusion (stars)Contact ForcesContact ForcesMany forces are due to contact between objects.Many forces are due to contact between objects.•Kick a ballKick a ball•Push with a bulldozerPush with a bulldozer•Tug from a ropeTug from a rope•Friction due to the groundFriction due to the groundThe actual force is electricity, but the atoms are so The actual force is electricity, but the atoms are so small we can treat the forces as coming from contact small we can treat the forces as coming from contact by larger objects.by larger objects.Newton’s Laws Newton’s Laws Ancient scientists looked to the Ancient scientists looked to the natural properties of objects.natural properties of objects.Motion was a result of the object’s Motion was a result of the object’s properties.properties.Newton defined motion based on Newton defined motion based on forces acting from outside an object.forces acting from outside an object.Three laws were used to define the Three laws were used to define the behavior of forces on objects.behavior of forces on objects.Law of InertiaLaw of Inertia1An object continues at rest, or in uniform motion in a An object continues at rest, or in uniform motion in a straight line, unless a force is imposed on it.straight line, unless a force is imposed on it.This describes constant velocity, so no acceleration.This describes constant velocity, so no acceleration.No acceleration means no force, and vice versa.No acceleration means no force, and vice versa.FFnetnet = 0 = 0  a = 0 (Newton’s first law). a = 0 (Newton’s first law).rocketno forceconstant velocityInertial Reference FramesInertial Reference FramesNo acceleration can mean an object at rest.No acceleration can mean an object at rest.No acceleration can also mean a constant velocity.No acceleration can also mean a constant velocity.Newton’s laws remain the same for observers at rest Newton’s laws remain the same for observers at rest or at a constant velocity.or at a constant velocity.An observer cannot use physics to distinguish An observer cannot use physics to distinguish between between inertial reference framesinertial reference