P2.2 Flashcards
In an interaction pair …
- Each force acts on a different object
- The forces are the same size and type
- the forces act in opposite directions
What is Newton’s third law?
“For every action there is an equal and opposite interaction”
Forces always come in pairs
What is a non-contact force?
A force produced because an object is in a field
The objects don’t need to be in contact for the force to act
Examples of non-contact forces
Electrostatics
Magnetism
Gravity
- these forces are the result of field
What is a contact force?
Forces that only act when objects are in contact
What happens to the atoms during a contact-force?
The bonds between atoms act like spring
You compress the bonds when you exert a force
Example of contact forces
Friction Drag Normal contact force Upthrust Tension
What is the interaction pair for friction on a sliding box and what is the mechanism that produces it?
Interaction pair: -The force of the box on the surface -The force of the surface on the box Mechanism The atoms that make up the surface interact when rough surfaces slide over each other
What is the interaction pair and mechanism that produces drag on a falling leaf
Interaction pair : The force of the falling leaf on the air The force of the air on the leaf Mechanism: The particles of the liquid or gas collide with the object and the object pushes them away
What is the interaction pair and the mechanism that produces normal contact force acting on an elephant
Interaction pair: The force of the elephant on the ground The force of the ground on the elephant Mechanism: Solid objects deform slightly when you exert a force on them. The binds between the particles are compressed.
What is the interaction pair and the mechanism that is produces upthrust on a floating boat
Interaction pair: The force of the boat on the water The force of the water on the boat Mechanism: Gravity produces pressure differences in a fluid. This pressure produces a net upwards force.
What is the interaction pair and mechanism that produces tension in the chord of a bungee jumper
Interaction pair:
The force of the bungee jumper on the bungee cord
The force of the bungee cord on the bungee jumper
Mechanism:
Solid objects deform slightly when you exert a force on them. The bonds between the particles are stretched
What does normal mean?
It means the force acts at right angles to the surfac
What is a free body diagram
It is a diagram that shows the forces acting on a single object
You can use the diagram to predict or explain the motion of the object or do to calculations
What is Newton’s first law?
“An object will continue to stay at rest or move with uniform velocity unless a force acts on it”
It takes a resultant force to change the motion (the speed or direction) or an object
If the resultant force is 0 the speed or direction of an object won’t change
True or false
True
What is inertia
It is a measure of how difficult it is to change the velocity of an object
How do you calculate momentum?
Momentum = mass X velocity
(Kgm/s2) = (kg) X (m/s)
What is the conservation of momentum?
In any collision momentum is conserved so the momentum before is equal to the momentum afterwards
What happens in an elastic collision?
No energy is transferred to other stores. The energy in the kinetic stores stays the same.
In reality some energy is transferred to a thermal store by sound so the collision isn’t perfectly elastic.
What happens when objects collide and move apart (an inelastic collision)?
In an inelastic collision some energy is transferred to other stores.
An example is a collision after which the velocity of combined objects is less than that of the original object.
What can a resultant force do?
It can…
- change the speed of an object
- change the direction of motion of an object
- change both the speed and direction of motion of an object
What is Newton’s second law
If the resultant force is not 0 the motion of an object changes.
Calculating force
Force (N) = mass (Kg) x acceleration (m/s)2
How do you explain the motion of falling objects? (Example of a skydiver)
- When you jump out of a plane you accelerate
- your motion changes because there is a resultant force on you
- the air exerts a force on you but the earth exerts a larger force
- as you accelerate the force of the air increases
- eventually the force of the air and earth are equal and your motion doesn’t change
-you have reached terminal velocity
A parachute increases the force of the air to reduce your velocity
How do you explain the motion of rockets
- When a rocket takes of there is a resultant force on it that produces a large acceleration
- the burning fuel pushes exhaust gases out of the bottom of the rocket. The gases pushing in the rocket and the rocket pushing on the gases are an example of Newton’s 3rd law,
- when the force of the gases on the rocket is bigger than the force of the Earth on the rocket then the rocket will accelerate
What is work?
Doing work is about using forces to transfer energy between stores.
How do you calculate work done?
Work done (J) = Force (N) X distance (M)
What is power?
Power tells you the rate at which energy is transferred.
How do you calculate power?
Power (W) = work down (J) ➗time (s)
