Module 3 - Section 5 (Newtons laws, forces and momentum) Flashcards
What is a force?
A push or pull force that acts on an object due to the interaction with another object
What are forces categorised under?
A vector
- direction and magnitude
What are contact forces?
PHYSICALLY TOUCHING
-friction
-drag/air resistance
-tension
-thrust
-contact
What are non-contact forces?
PHYSICALLY SEPERATED
-gravitational
-electrostatic
-magnetic
How does forces come into play when a pen is dropped?
-A gravitational force acts on the mass of the pen causing it to accelerate towards the ground
Whats the equation linking force acceleration and mass
F = m x a
Whats the difference between mass and weight?
Mass is a physical property as in the amount of something (kg)
Weight is the downward force due to gravity acting on the mass (n)
How do you find the centre of mass of an object?
MODELLING
Method:
-Cut out an irregular shape
-Cut 3 holes around the edge of the card
-hang the card through a nail on a clamp stand and draw on a straight line using weighted string
-hang the shape from the other holes repeating the same steps
-the place where the lines intercept is the centre of mass
NOTE: the centre of mass is not always on the shape.
What does it mean when an object is in equilibrium?
The sum of the anti-clockwise moments = the sum of the clockwise moments
What is the equation for moments?
Moment = force x distance from pivot
What factors influence the drag force in a liquid?
SA
Velocity
Density of fluid
How is terminal velocity changed?
SA: greater the SA = the greater the drag force so lower terminal velocity
Mass: greater mass = greater weight, so a larger drag force os required to equal the weight so a higher terminal velocity.
What is density?
The mass per unit volume
Density = mass / volume
What is the equation for pressure?
Pressure = Force / Area
What is the rule about fluid pressure?
At a greater depth the pressure is larger
How can the pressure in a fluid be calculated?
P = ⍴ h g
Pressure = density x depth x g (9.81)
How can you derive the fluid pressure equation?
P = F/A
F = W = mg Therefore: P = mg/A
A = V/h Therefore: P = mgh/V
⍴ = m/V Therefore: P = ⍴hg
P = ⍴ h g
When an object is floating in equilibrium what are the two things that are equal?
The upthrust and the weight
What is Archimedes Principle?
The upthrust exerted on a body immersed in a fluid (whether fully or partially submerged) is equal to the weight of the fluid the body displaces.
What is Newtons First law?
An object at constant velocity will remain at constant velocity until an external force acts on it.
It will remain at rest until a resultant force acts upon it (unbalanced)
What is Newtons Second law?
F = ma
Acceleration is produces when a force acts on a mass and unbalances the forces.
What is Newtons Third law?
Every action has an equal and opposite reaction force
- This MUST be the same size and same type of force acting in different directions.
What is Momentum?
Momentum = mass x velocity
What is the rule about momentum?
When objects collide the total momentum is conserved within the closed system as long as no external forces act on it.
Total momentum before = total momentum after
What is a perfect elastic collision?
When there is no loss of kinetic energy eg: particle collisions
What is an inelastic collision?
When kinetic energy is lost to other energy sources eg: sound and heat like car crashes.
How would you calculate the change in momentum?
Momentum = Force x time
