Forces Notes PDF

What is a force? A force is a push or pull upon an object resulting from its interaction with another object. Unit of force Effects of forces...

What is a force? A force is a push or pull upon an object resulting from its interaction with another object. Unit of force Effects of forces Forces work in pairs Newton (N) Named after Sir For every action force there is an Change in shape Isaac Newton equal and opposite reaction force. Action and reaction forces are Squeeze equal in magnitude but opposite in Stretch direction. Measuring force The action and reaction forces are on Change in motion Measured using a spring different objects. balance. Start The action and reaction forces can’t Meter has a spring that cancel each other out. Stop stretches when a force is EXAMPLE: Speed up applied. When you push on a wall, the wall pushes back on you with an equal force Slow down The amount of ‘stretch’ is proportional to the size of Change direction the force. © Material designed by Curro Digital Learning. No part of it can be used without express written permission. Created by M Woolward.  Types of forces Contact forces Non-contact or field forces These are forces that occur when objects are physically These are forces that can occur over a distance. They occur in a touching each other. region (field) surrounding a particular object. Frictional force Gravitational force Occurs when two Magnetic force The force of attraction between surfaces slide or try to two objects with mass. slide across each other. The force of attraction Tension force or repulsion due to A gravitational field is the Opposes the motion of interacting magnetic region around a mass where A pulling force acting the objects. fields. another mass experiences a through a string, rope, gravitational force. cable, or wire when it is Opposite poles attract Normal force each other, while like pulled tight. The support force poles repel each other. Electrostatic force exerted by a surface Applied force Like charges repel each other, Magnets attract perpendicular to the and opposite charges attract A force that is applied ferromagnetic materials object resting on it. each other to an object by a like steel, iron, nickel, person or another and cobalt. Air resistance A charged object can attract object. a neutral object. The force that acts on objects as they move An electric field is the region around through the air. a charged particle or object.  Representing forces Force diagram Free body diagram Shows an object with all the forces acting on it. Shows the object as a dot with all the forces acting on it. Object can be simplified as a block. Object is represented by a dot. Arrows are used to represent each force. Arrows are used to represent each force. The length of the arrow is indicative of the size of the force. The length of the arrow is indicative of the size of the force. The arrow points in the direction of the force. The arrow points in the direction of the force. The arrow starts at the position where the force is exerted. All arrows start at the dot and points away from the dot. The arrow must touch the block. The arrow must touch the dot. The arrow should be clearly labelled with the name of the force. The arrow should be clearly labelled with the name of the force. normal force normal force scenario applied force frictional force applied force frictional force gravitational force (weight) gravitational force (weight) © Material designed by Curro Digital Learning. No part of it can be used without express written permission. Created by M Woolward.  Resultant or net force The single force that will have the same effect as all the original forces acting on an object. Net force = 0 Net force = 0 Balanced forces Unbalanced forces The effects of each force are cancelled out by another. The effects of the forces are not cancelled out by other forces. When forces are balanced an object is in equilibrium. Results in a change in the motion of the object. Static equilibrium: Object remains at rest. The object can start moving, stop moving, change direction, speed up, or slow down. Dynamic equilibrium: Object continues to move at constant velocity. EXAMPLE: A soccer ball being kicked, where the applied force from Constant velocity: The object’s speed and direction the kick overcomes the forces of friction and gravity, remains the same. causing it to accelerate. EXAMPLE: A book resting on a table experiences balanced forces. The gravitational force pulling it down is balanced by the normal force pushing it up. © Material designed by Curro Digital Learning. No part of it can be used without express written permission. Created by M Woolward.  Contact forces These are forces that occur when objects are physically touching each other. Frictional force Applied force A force that is applied to an object by a friction) often in physics. You will use these (with person or another object. Occurs when two surfaces slide or The support force exerted by a surface try to slide across each other. Normal force perpendicular to the object resting on it. Opposes the motion of the objects A pulling force acting through a string, and acts parallel to the surface Tension force rope, cable, or wire when it is pulled tight. The force that acts on objects as Air resistance they move through the air. Static friction Kinetic friction The force that keeps The force that slows Compression, torsion, and shear forces are different types of forces that can an object from down an object that act on objects, changing their shape or structure. moving when you try is already moving. to push it. This force pushes or squeezes an object, Acts when the object Compression force making it shorter or thicker. Acts when the object is sliding. It is weaker is not moving. It than static friction. This force causes parts of an object to slide needs to be Shear force past each other in different directions. overcome to start the motion. Torsion force This is a turning or twisting force. © Material designed by Curro Digital Learning. No part of it can be used without express written permission. Created by M Woolward.  Magnetic force A non-contact force that can act at a distance due to the magnetic field produced by the magnets. Ferromagnetic materials Types of forces Magnetic field Iron (Fe) Unlike poles attract. The region around a magnet where magnetic forces can be felt. Nickel (Ni) Like poles repel. Magnetic field lines represent Cobalt (Co) A magnet will attract a non- the direction and strength of a magnetised ferromagnetic material magnetic field. Alloys containg iron, nickel, or cabalt (e.g, steel) regardless of the pole because the Field lines go from north to south magnet's magnetic field induces a on the outside of a magnet. temporary alignment of magnetic domains in the material, creating a Closer lines show a stronger Magnet polarity temporary north and south pole that magnetic field. is attracted to the magnet. Magnets have two poles. Field lines never cross. North pole (N): The end of the magnet that points towards Magnetic field diagrams the Earth's northern magnetic Around a single bar magnet Between two like poles Between two opposite poles pole when freely suspended. South pole (S): The end of the magnet that points towards the Earth's southern magnetic pole when freely suspended.  Gravitational force The attractive non-contact force that acts between any two objects with mass. Dependends on... Comparing... mass distance Mass Weight The gravitational The gravitational force Gravitational force exerted on an object force between two decreases as the The amount of matter in an by a large celestial body (like Earth) on or objects increases distance between the object. near its surface. with the mass of centres of the objects the objects. increases. Symbol > m Symbol > W or Fg Gravitational acceleration Measured in kilograms (kg). Measured in Newtons (N). The acceleration of an object due to the gravitational pull of a massive body like Earth. Weight depends on the gravitational Mass is constant and does not acceleration of the location and On Earth, the gravitational acceleration is change with location. therefore can change with location. approximately 9,8 m.s-2. Weight is a vector quantity (has both Calculating weight Mass is a scalar quantity (has magnitude and direction). magnitude but no direction). E.g. 20 N, towards Earth © Material designed by Curro Digital Learning. No part of it can be used without express written permission. Created by M Woolward.  Electrostatic force The attractive or repulsive non-contact force that acts between charged particles or objects. Types of forces Discharge The release of built-up static Attractive force Repulsive force electricity between two objects with different electric potentials. Between oppositely charged objects. Between like-charged objects. Between a charged object and a neutral object Law of conservation of charge Electric charge cannot be created or Charging methods destroyed; it can only be transferred from one object to another. friction induction Rubbing different materials Polarisation together results in electron A charged object close transfer. to a neutral object. It occurs when the electric field conduction of a charged object causes the Material that gains electrons The charged object's charges within a nearby neutral becomes negative. A charged object comes electric field causes object to rearrange, creating Material that loses into direct contact with a polarisation in the regions of positive and negative electrons becomes neutral object. neutral object. charge within the neutral object. positive. © Material designed by Curro Digital Learning. No part of it can be used without express written permission. Created by M Woolward.