1 / 21

Force

Force. Force is a push or pull on an object The object is called the System Force on a system in motion causes change in velocity = acceleration Force is a vector, it has direction External World = everything around the system that exerts a force. Types of Forces. Forces Contact

debbie
Download Presentation

Force

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Force • Force is a push or pull on an object • The object is called the System • Force on a system in motion causes change in velocity = acceleration • Force is a vector, it has direction • External World = everything around the system that exerts a force

  2. Types of Forces Forces Contact • When the external world is in contact with the system and exerts a force ex. Hand that pushes, Rope that pulls Field Forces • A force exerted on a system without touching the system ex. Gravity, Magnetic force, Interaction between charged particles

  3. Agent • An agent is the item in the external world that causes the force to act on the system • ex. The hand that holds The rope that pulls The earth The magnet

  4. Free Body Diagram • A diagram representing the System, Agent and the Forces acting on the system • System is represented by a dot • Forces represented by arrows pointing in the direction of the force, away from system • Label each force with a subscript • Choose direction of +ve usually towards stronger force

  5. String Positive Direction Ball (force of tension) Ft (force of gravity) F g

  6. Combining Forces • As forces are vectors they can be added just as vectors ex.1 Fa + Fb = F net ex.2 Fa + Fb = Fnet Nonlinear non perpendicular forces are added by adding x and y components of the force vectors

  7. Newton’s First Law • An object at rest will remain at rest and an object in motion will remain in motion unless acted on by an external net force • Also known as the Law of Inertia • Inertia is the tendency of an object to resist change in motion • Equilibrium = if the net force on a system is zero the system is in equilibrium speed and direction is unchanged.

  8. Common Types of Forces • Friction Ff = Contact force opposing motion of two surfaces, parallel to the surface and opposite to the direction of motion • Normal FN = Contact force exerted by system’s surface perpendicular to and away from surface • Spring F sp = A restoring force- push or pull of spring exerted on system opposite to displacement

  9. Tension FT = pull exerted by a rope on a system, away from the system and parallel to the rope • Thrust FTHRUST = a force that moves a system in the same direction as the acceleration • Weight F g = a field force on a system due to gravity directed to the center of the earth

  10. Newton’s Second Law • The acceleration of an object is equal to the net force acting on it divided by the mass of the object a = F/m or F = ma • The larger the force the greater the acceleration The greater the mass with the same force the lower the acceleration • Force of 1N = 1kg * 1m/s.s

  11. Newton’s Third Law • All forces come in pairs equal and opposite in direction • ex. A ball on a table and the table on the earth. Forces-ball on table / table on ball -table on earth/ earth on table - ball on earth/ earth on ball

  12. Net free body diagram ball table earth F table on ball F earth on ball

  13. Drag Force and Terminal Velocity • Drag Force is the force exerted on an object as it moves the a fluid ex. Air and water • as the speed of the object through the fluid increases so does the drag • Drag is effected by the fluids viscosity and temperature • Terminal velocity is when the drag force equals the force due to gravity no acceleration constant velocity app.(60m/s)

  14. Tension • Is a force exerted by a string or rope on a system • It is assumed the rope has no mass • Tension within all points of the rope is equal and opposite to the force exerted by the system’s weight

  15. Example of bucket on rope FT Fg =mg

  16. Normal Force • Is a contact force exerted by a surface on an object. This force is perpendicular to the surface of contact N Fg

  17. Gravitational Force • Gravitational force is the mutual attraction between any two bodies in the universe • Newton’s Law of Universal Gravitation =every particle in the universe attracts every other particle with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them • F g = Gm1m2/r2 where G = the universal gravitational constant = 6.67*10-11N.m2/kg2

  18. Gravity • As weight = mg then w = GMEm/r2 • Then g = GME/r2 • Therefore the larger the mass of an object the larger the effective gravity it generates

  19. Forces of Friction fs and fk • An object moving on a surface or passing through a fluid experiences resistance to motion = friction • F fs = forces of static friction = the force that prevents movement of an object that is being subjected to an external force • When movement is about to occur fs is at max.

  20. fs and f k • When a force F exceeds Ffs max then movement will occur and the new friction force is less. This new friction force is called the Force of kinetic friction fk • When F-fk= positive value there is acceleration • Both fs and fk are proportional to the normal force; fs=usn and fk=ukn • us is the coefficient of static friction • Uk is the coefficient of kinetic friction

  21. Solving Friction Problems • Draw a free body diagram making sure to label all forces

More Related