Topic 5 - Forces (5) Flashcards by Hattie Wilson

MOMENTS:
What is a moment?

the turning effect of a force

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MOMENTS:
What happens if the total clockwise moment equals the total anticlockwise moment about the pivot?

the object is balanced and won’t turn

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MOMENTS:
How do levers make it easier for us to do work?

they increase the distance from the pivot at which the force is applied. beacause M = Fd this means less force is needed to get the same moment
this makes it easier for us to do work (e.g. lift a load or turn a nut)

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MOMENTS:
What are gears?

circular discs with teeth around their edges

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MOMENTS:
How do gears work?

their teeth interlock so that turning one causes another to turn in the opposite direction

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MOMENTS:
What are gears used for?

to transmit the rotational effect of a force from one place to another

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MOMENTS:
How do different sized gears work?

they can be used to change the moment of a force
a force transmitted to a larger gear will cause a bigger moment, as the distance to the pivot is greater

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MOMENTS:
Do smaller or larger gears turn faster?

a larger gear will turn slower than a smaller gear

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NEWTON’S FIRST LAW:
What does newton’s first law say?

if the resultant force on a stationary object 0, the object will remain stationary.
If the resultant force on a moving object is 0, it’ll just carry on moving at the same velocity (same speed and direction)

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NEWTON’S FIRST LAW:
What does newton’s first law mean?

a resultant force is needed to make something start moving, speed up or slow down

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NEWTON’S FIRST LAW:
When any vehicle is moving at a constant velocity, what must be balanced?

the resistive and driving forces

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NEWTON’S FIRST LAW:
When does the velocity of a vehicle change?

if there is a non-zero resultant force acting on the object
(the arrows on a free body diagram will be unequal)

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NEWTON’S FIRST LAW:
What does a non-zero resultant force always produce?

acceleration (or deceleration) in the direction of the force

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NEWTON’S FIRST LAW:
What 5 forms can acceleration (from a non-zero resultant force) take?

starting, stopping, speeding up, slowing down, changing direction

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NEWTON’S SECOND LAW:
What is the relationship between resultant force and acceleration?

they are directly proportional
the larger the resultant force acting on an object, the more the object accelerates

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NEWTON’S SECOND LAW:
What is the relatonship between acceleration and the mass of the object?

inversely proportional
an object with a larger mass will accelerate less than than one with a smaller mass (for a fixed resultant force)

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INERTIA:
What is inertia?

the tendency for motion to remain unchanged (to continue in the same state of motion)

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INERTIA:
What does an object’s inertial mass measure?

how difficult it id to change the velocity of an object

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INERTIA:
How can inertial mass be found?

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using newton’s second law of F = ma.
Rearranging this gives m = f/a , so inertial mass in just the ratio of force over acceleration

NEWTON’S THIRD LAW:
What does Newton’s third law say?

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when two objects interact, the forces they exert on each other are equal and opposite

NEWTON’S THIRD LAW:
Why is a book’s weight on a table and the equal normal contact force not an example of newton’s third law?

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the two forces are different types and both acting on the book
(the book is in equilibrium)

FLUID PRESSURE:
What are fluids?

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liquids and gases
substances that can flow because their particles are able to move around

FLUID PRESSURE:
How do fluids exert pressure?

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the particles move around, tey collide with surfaces and other particles
as they have a mass they exert a force on the object they collide with
pressure is force per unit area, so this means the particles exert a pressure
the pressure of a fluid means a force is exerted normal (at right angles) to any surface in contact with the fluid

FLUID PRESSURE:
In what direction, do fluids exert pressure?

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a force is exerted normal (at right angles) to any surface in contact with the fluid

FLUID PRESSURE: What does the pressure in a liquid depend on? (2)

- density of the liquid - depth of the liquid

FLUID PRESSURE: What is density a measure of?

the 'compactness' of a substance, i.e. how close together the particles in a substance are

FLUID PRESSURE: What is density like for a given liquid?

- density is uniform (the same everywhere) - it doesn't vary with shape of size (but the density of a gas can vary)

FLUID PRESSURE: How does density of a liquid affect the pressure it exerts? (the more dense...)

- the more dense a given liquid is, the more particles it has in a certain space - this means more particles are able to collide so the pressure is higher

FLUID PRESSURE: How does the depth of a liquid affect the pressure it exerts?

- as the depth of a liquid increases, the number of particles above that point increases - - the weight of these particles adds to the pressure felt at that point, so liquid pressure increases with depth

FLUID PRESSURE: Why can we assume density in a liquid is uniform?

even though they can be squashed slightly under a very large pressure , the change is very small

FLUID PRESSURE: What is gravitational field strength on earth?

9.8 N/kg

UPTHRUST AND ATMOSPHERIC PRESSURE: What happens when an object is submerged in a fluid (either partially or completely)?

the pressure of the fluid exerts a force on it in every direction objects in fluids experience upthrust

UPTHRUST AND ATMOSPHERIC PRESSURE: Where is the force exerted on an object in a fluid greater?Why?

- the force exerted on the bottom of an object is greater than the force exerted on the top of an object - pressure increases with depth

UPTHRUST AND ATMOSPHERIC PRESSURE: What causes objects in fluid to feel upthrust?

- the force exerted on the bottom of the object is greater than on the top (pressure increases with depth) - this causes a resultant force upwards, known as upthrust (upthrust is equal to the weight of the fluid that has beeen displaced)

UPTHRUST AND ATMOSPHERIC PRESSURE: What is the upthrust experienced by a submerged object equal to?

the weight of the fluid that has been displaced by the object

UPTHRUST AND ATMOSPHERIC PRESSURE: What needs to happen for an object to float?

the upthrust on an object is equal to it's weight, then the forces balance out and the object floats

UPTHRUST AND ATMOSPHERIC PRESSURE: What happens when a submerged object's weight is greater than the upthrust?

the object sinks

UPTHRUST AND ATMOSPHERIC PRESSURE: What does whether an object floats or not depend on?

the density of the object

UPTHRUST AND ATMOSPHERIC PRESSURE: What happens when an object is less dense than the fluid it is placed in?

- the object weighs less than the equivalent volume of liquid - so it displaces a volume of fluid that is equal to its weight before it is completely submerged - at this point the object's weight is equal to the upthrust, so the object floats

UPTHRUST AND ATMOSPHERIC PRESSURE: What happens when an object is more dense than the fluid it is placed in?

- it is unable to diplace enough fluid to equal it's weight - its weight is always larger than the upthrust, so it sinks

UPTHRUST AND ATMOSPHERIC PRESSURE: Explain how submarines make use of upthrust?

- to sink, large tanks are filled with water to increase the weight of the submarine so it is more than the upthrust - to rise to the surface, the tanks are filled with compressed air to reduce the weight so that it's less than the upthrust

UPTHRUST AND ATMOSPHERIC PRESSURE: What is the atmosphere?

a layer of air that surrounds earth (it is thin compared to the size of earth)

UPTHRUST AND ATMOSPHERIC PRESSURE: How is atmospheric pressure created on a surface?

by air molecules colliding with the surface

UPTHRUST AND ATMOSPHERIC PRESSURE: What is the relationship between altitude and atmospheric pressure?

as altitude increases, atmospheric pressure decreases

UPTHRUST AND ATMOSPHERIC PRESSURE: Why does atmopheric pressure decrease as altitude increases?

as altitude increases, the atmosphere gets less dense, so there are fewer air molecules able to colllide with the surface - there are also fewer molecules above a surface as the height increases, so the weight of air above it, which contributes to atmospheric pressure, decreases with altitude

Topic 5 - Forces (5) Flashcards

(45 cards)