Topic 9 - Forces and their effects Flashcards
Examples of object interaction
Gravitational attraction– an attraction between two objects with mass, the larger mass gives greater attraction
o Electrostatic attraction/repulsion –Larger charge gives greater force Like charges repel, opposite charges attract
o Magnetic attraction/repulsion – stronger magnet gives stronger field, having a greater force Like poles repel, opposite poles attract
Examples of interaction objects w/ contact
Normal contact force
▪ The force is perpendicular to the plane of contact
o Friction
▪ Surfaces that are rough cause friction when moved
Describe a vector and examples
- they have size and direction
– e.g. Weight, velocity, force, displacement, etc.
Describe a free body diagram ( vector diagrams)
- reaction force
- friction
- weight
- it Shows the direction of forces that are present in a
situation
-reaction force always acts at the normal to the
line of contact, from the point of contact - Friction acts in the opposite direction to movement,
- Weight always acts downwards, acting from Centre
of Mass
Describe scale drawings ( vector diagrams)
The length of each arrow represents its size (in relation to the other forces acting on the object)
- direction with larger arrows shows resultant force
- If arrows are in opposite directions with equal
length
- they’re Equal in magnitude but opposite in direction
- The forces cancel out
- the object is in equilibrium
- it travels at a constant velocity
Describe what happens if there is a low amount of drag
diagram
- if the drag is a lot less than the weight, the resultant force causes him to accelerate
Describe an isolated system and examples
- it means no forces are present that come from a source outside the system
- e.g. a magnetic ball just rolling down a hill, an external force would be a magnet at the top of the hill
Forces present while skydiving ( there are only 2)
- air resistance and weight
Describe how forces are used whilst skydiving ( the process)
- Initially, the skydiver has no air resistance and the only force acting on him is weight
- As he falls, he accelerates, increasing his speed
- This makes air resistance increase
- so the resultant force decreases
- acceleration decreases as F=ma, so he is not speeding up as quickly
- Eventually weight and air resistance are equal and balanced, so there is no resultant force
- there is no acceleration and terminal velocity is reached
What is terminal velocity
- maximum velocity attainable by an object as it falls through a fluid e.g. air .
- occurs when the drag force and the buoyancy/upthrust is equal to the downward force of gravity acting on the object.
Describe forces acting on a moving vehicle
- Initially, low air resistance and thrust is only hindered by friction
- Air resistance increases, decreasing the resultant force
- Eventually the car is travelling at terminal velocity, where the thrust is balanced by drag and friction, so there is no resultant force
- This changes when more thrust is added, as it now becomes the resultant force until the drag increases to balance it again
Rotation occurs…
pivot point
If an object is attached to a pivot point
o A point which it can rotate about, but cannot move away from
-And a force is applied not towards the point
o The object won’t rotate, and will just be held still, because there’s no resultant force
Rotation occurs…
perpendicular to object
If the force is applied perpendicular to the object
o It will move about the pivot in that direction
Rotation occurs…
not perpendicular to object
If the Force is applied not perpendicular to the object
o Need to find perpendicular distance from pivot to line of force
o See which direction it will turn
Moment of a force (N) equation
Moment of a force (N) = force (N) × distance perpendicular to the direction of the force (m)
