Chapter 4

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forces in action

6 Terms

1
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force and acceleration

  • the mass is the property of an object

  • the resultant force will cause an object to accelerate

  • F=ma - newton’s second law of motion - m - inertial mass(objects have a tendency to resist an change in motion)

  • `newton’s 3rd law - opposing forces have to be of the same type - eg equal and opposite force of your weight on the earth is the gravitational force you have on the earth, and the normal contact force is opposed by the reaction force of the other object


2
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centre of mass

  • an imaginary point at which where the entire mass of an object appears to act

  • any object will come to rest if it’s centre of mass is directly below it’s point of suspension

motion

  • if a force acts on an object through it’s centre of mass than the object will move in a straight line with acceleration or not - if there is a resultant force or not

  • if not acting through centre of Nass then the object will have additional rotational motion - turning effect introduced acting at a distance from centre of mass

how to find centre of gravity

  1. make 3 holes in random places along the edge

  2. hang the shape from the first hole by placing it through ping - let the shape swing + come to rest

  3. use a plumb line to draw a vertical line down the point of suspension to the bottom of the shape

  4. repeat step 2 + 3 but from a different hole

  5. point of intersection is the centre if mass but if leaves a triangle centre of mass is assumed centre of the triangle


stability

  • objects that have a wide base but low centre of mass are more stable than vice versa

  • an object will become unstable when the object is tilted so that centre of mass lies outside the wid


3
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free body diagrams

  • arrows + labels in the direction of the force

  • touching the object

  • simple shapes


4
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free body diagram of car on a slope

  • assuming no friction - only forces acting is the weight and normal contact force

  • by resolving weight only horizontal component is responsible for the acceleration of the object

  • no acceleration in the vertical component so NCF = vertical component

  • (friction can also be thwarted driving force)


<ul><li><p>assuming no friction - only forces acting is the weight and normal contact force</p></li><li><p>by resolving weight only horizontal component is responsible for the acceleration of the object</p></li><li><p>no acceleration in the vertical component so NCF = vertical component</p></li><li><p>(friction can also be thwarted driving force) </p></li></ul><p></p>
5
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5 types of forces

tension

  • experienced by rope, cable or wire that is being hung rotated or supported

  • can cause objects to accelerate or change shape

normal contact/reaction force

  • the force that acts perpendicular to the point + the surface which it is in contact

upthrust

  • the upwards force that a liquid/gas exerts on a body floating due to the water displaced

  • a body falling through any fluid will experience drag + upthrust

friction

  • occurs between 2 surfaces in contact with on another - caused by interatomic + intermolecular forces when surfaces are in contact

  • friction opposes motion at the point of contact


<p>tension </p><ul><li><p>experienced by rope, cable or wire that is being hung rotated or supported </p></li><li><p>can cause objects to accelerate or change shape </p></li></ul><p>normal contact/reaction force </p><ul><li><p>the force that acts perpendicular to the point + the surface which it is in contact </p></li></ul><p>upthrust </p><ul><li><p>the upwards force that a liquid/gas exerts on a body floating due to the water displaced </p></li><li><p>a body falling through any fluid will experience drag + upthrust </p></li></ul><p>friction </p><ul><li><p>occurs between 2 surfaces in contact with on another - caused by interatomic + intermolecular forces when surfaces are in contact </p></li><li><p>friction opposes motion at the point of contact </p></li></ul><p></p>
6
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triangles of forces

  • connect all the vectors - triangle is closed as no resultant force so object is in equilibrium - all the coplanar(forces in the same plane) are balanced

  • resultant force in horizontal and vertical component must be 0 so can resolve the force T however any pairs of the forces must add together to e the same force as the 3rd.



<ul><li><p>connect all the vectors - triangle is closed as no resultant force so object is in equilibrium - all the coplanar(forces in the same plane) are balanced </p></li><li><p>resultant force in horizontal and vertical component must be 0 so can resolve the force T however any pairs of the forces must add together to e the same force as the 3rd. </p></li><li><p></p></li></ul><p></p>