Forces (Seneca) Flashcards
Scalar quantities only have a …
magnitude (size).
Speed is a ——— quantity.
scalar
Scalar quantities, like speed, do not have a …
direction
Velocity describes …
an object’s direction as well as its speed.
Velocity is a vector quantity because …
it has a magnitude (or size) and a direction.
The average speed (measured in metres per second, m/s) is equal to the …
distance travelled (metres, m) divided by the time taken (seconds, s).
Average speed =
total distance / total time
If two people stand back-to-back and walk away from each other at the same speed, but in opposite directions, their speeds are the same but …
one will have a positive velocity and the other will have a negative velocity.
Velocity describes an object’s ———- as well as its speed.
direction
————- theorem is used to work out the resultant force.
Pythagoras’
Acceleration =
Change in velocity / time taken
Displacement is the …
distance an object moves in a straight line from a starting point to a finishing point.
Displacement is a ——— quantity.
vector
Distance is a ———- quantity.
scalar
Distance is …
how far an object moves.
A force is a …
push or a pull that acts on an object when it interacts with another object.
All forces between objects are either:
- Contact forces
- Non-contact forces
Contact forces happen when …
two objects are physically touching.
———- are all examples of contact forces.
Friction, air resistance, tension and normal contact force
Non-contact forces happen when …
objects are separated (not touching).
———— are all examples of non-contact forces.
Gravitational force, electrostatic force and magnetic force
Tension is …
the pulling force that a string or cable exerts (creates) when something or someone pulls on it.
When you push on a table, your hand doesn’t move through it.
This is because …
the normal contact force from the table pushes equally on your hand.
Air resistance comes about when …
an object moves through the air and collides with (hits) air molecules.
Friction comes about whenever …
two surfaces are touching and try to move against each other.
Tiny bumps in the surface ——————. This creates a frictional force that opposes their motion.
interlock (overlap or fit together)
An interaction pair is a …
set of 2 forces that are equal and opposite, acting on 2 interacting objects.
Distance-time graphs have distance on the 1. and time on the 2.
- y-axis
- x-axis.
On a distance-time graph, motion (movement) at a constant speed is shown by a …
straight line.
On a distance-time graph, If the line is horizontal, then the object is …
stationary
On a distance-time graph, If an object is accelerating, we can measure its speed by …
drawing a tangent and measuring the gradient of the distance-time graph at that point.
Speed-time graphs have speed on the 1. and time on the 2.
- y-axis
- x-axis
Velocity-time graphs would simply have ———- on the y-axis instead of speed.
velocity
If an object slows down, its graph will have a ——— gradient.
negative
The area under a velocity-time graph is equal to the …
distance travelled by an object.
On a distance-time graph, if the object moves faster, the gradient becomes …
steeper
On a speed-time graph, A curved line shows that an object is …
accelerating or decelerating at a rate that is not constant.
Velocity =
Displacement/ time
If a velocity-time graph consists of one diagonal line in the downwards direction, what statements about the motion are true?
- the object is decelerating at a constant rate
- the object is travelling at a non-constant velocity
Objects that move in a circular path at a constant speed have ——— acceleration as their direction is constantly changing.
positive
The mass of an object is a measure of …
the amount of matter it contains.
The mass of an object is …
constant
An object’s mass is also a measure of …
how difficult it is to change the object’s motion.
An object’s mass is also a measure of how difficult it is to change the object’s motion.
This is called …
inertia
An object with a high mass has ——— inertia than an object with a lower mass.
more
It is difficult to move an object with a ———— , and once it is moving, the object’s motion is hard to stop.
high mass (and high inertia)
What is the name of the measure of how difficult it is to change an object’s motion?
Inertia
Although the mass of an object is spread out across its body, it is possible to find a …
single point where all of the mass appears to be.
Although the mass of an object is spread out across its body, it is possible to find a single point where all of the mass appears to be. This point is called …
the object’s centre of mass.
If an object is hung from a string, it will hang with its centre of mass directly …
below the point that it is hung from.
The centre of mass is the …
point through which an object’s weight appears to act.
An object will fall over if its …
centre of mass is outside its base.
An object will fall off a surface if its …
centre of mass isn’t over the surface.
A force may cause a mass to …
accelerate
A force may cause a mass to accelerate. This acceleration can be a …
change in speed, a change in direction or a change in both speed and direction.
The resultant force is the …
sum of all of the forces acting on an object.
The change in an object’s motion is caused by the …
resultant force.
If the forces acting on an object are unbalanced (not equal), it means that a — is acting on a object.
resultant force
Resultant force (F) =
mass (m) x acceleration (a)
What is Newton’s second law?
Resultant force (F) = mass (m) x acceleration (a)
The acceleration can be calculated with the following equation:
Resultant force (F) = mass (m) x acceleration (a)
If an object is stationary (not moving) and there is no resultant force acting on it, it will …
stay stationary.
When a vehicle is travelling at a steady speed, the resistive forces (such as friction and air resistance) are …
balancing the driving force.
When a vehicle is travelling at a steady speed, the resistive forces (such as friction and air resistance) are balancing the driving force.
When there are balanced forces, there is …
no resultant force.
Newton’s Third Law says that:
whenever 2 objects interact, the forces that they exert on (apply to) each other are equal and opposite.
If one object exerts (applies) a force on another object, then the other object must be …
exerting (applying) a force back.
A free body force diagram is a …
diagram showing the forces acting on an object.
A free body force diagram is a diagram showing the forces acting on an object. These are shown as …
vectors
We can use free body diagrams to work out the resultant force when more than one force is acting on an object. We can also use the diagrams to see if an object is in …
equilibrium
We can use free body diagrams to work out the resultant force when more than one force is acting on an object. We can also use the diagrams to see if an object is in equilibrium. If the resultant force is ——- , we say the object is in equilibrium.
zero
What is the term used for an object that has no resultant forces on it?
Equilibrium
We can split a force into —————— We can use grid lines to find the size of these forces.
horizontal and vertical parts.
We can stretch, bend or compress objects by applying forces to them.
For this to happen, there must be …
2 or more forces acting on an object.
We can stretch, bend or compress objects by applying forces to them.
For this to happen, there must be 2 or more forces acting on an object.
If only one force is acting, the object will …
just move in the direction of that force.
Objects can stretch, bend or compress objects by applying forces to them.
For this to happen, there must be 2 or more forces acting on an object.
If only one force is acting, the object will just move in the direction of that force.
Because of this, we can normally only stretch, bend or compress ————- objects.
stationary (still)
Objects can be deformed in 2 ways :
elastically and inelastically.
An elastically deformed object will …
return to its original shape when the force stops.
An inelastically deformed object will …
not return to its original shape when the force stops.
An extension-load graph has the —————- plotted on the y-axis, and the extension of the spring on the x-axis.
force acting on a spring
An extension-load graph has the force acting on a spring plotted on the y-axis, and the ————— on the x-axis.
extension of the spring
As the force on the spring increases, the spring reaches its limit of proportionality.
On the graph shown, this is where the line begins to …
curve.
Hooke’s Law tells us that the …
Force (measured in newtons, N) is equal to the spring constant (measured in N/m) times the spring extension (measured in metres, m).
What property of a spring does the spring constant represent?
Stiffness
Describe the investigation of Hooke’s Law.
Set up the apparatus as above.
First, measure the original length of the spring.
Next, hang different masses on the spring and measure the length of the spring in each case.
Adding masses to the spring increases the downwards force as each mass has weight.
The extension of the spring equals the length with masses minus the original length:
extension of the spring = length of the spring with masses − original length of the spring.
Plot a graph with the extension of the spring on the x-axis and force on the y-axis.
force =
spring constant x extension.
The limit of proportionality is the point where …
Hooke’s law breaks down.
The elastic potential energy stored in a spring is equal to the …
work done when stretching it.
The elastic potential energy stored in a stretched spring equals the ——— under the force-extension graph.
area
If an object is in free fall, then the …
object’s weight is the only force acting on it.
The weight of an object is the force that acts ———— on an object due to gravity.
downwards
The object hangs from the spring and is at rest so the resultant force must be zero:
mg=ke
mass of the object attached to the spring x the acceleration due to gravity = the spring constant x the extension of the spring
Substitute e into the formula for the elastic potential energy:
(M2 x g2)/ 2k = Eep
The average value for acceleration on Earth due to gravity is …
9.81 m/s2,
An object in free fall will accelerate at a ———— rate.
constant
An object in free fall will accelerate at a constant rate. This constant rate is called the acceleration due to …
gravity (g).
Which symbol is used to denote the acceleration due to gravity?
g
Objects falling through the Earth’s atmosphere do not continue to accelerate indefinitely because …
air resistance slows them down.
Air resistance slows down a falling object.
The force due to air resistance increases as the …
speed of a falling object increases.
Air resistance is a …
frictional force that opposes the motion of objects moving quickly through the air.
Features of air resistance:
- Is a frictional force
- Slows a falling object
- Opposes the motion (movement) of objects moving through air
If an object falls without air resistance, the distance-time and speed-time graphs look like what?
- The speed-time graph for the object is a straight line with a constant slope, showing that the object’s acceleration is constant.
- The slope of the speed-time graph has a value equal to g (the object’s acceleration due to gravity).
On the speed-time graph for an object in free fall, what will it be equal to?
The gradient/slope
An object’s speed increases as it accelerates due to gravity.
This increase in speed causes an increase in air resistance, because …
it opposes the motion (fall).
An object’s speed increases as it accelerates due to gravity.
This increase in speed causes an increase in air resistance, which opposes the motion (fall).
The air resistance increases until it equals …
the weight (force due to gravity) of the object.
Once the weight force and force due to air resistance are equal, the object …
stops accelerating - it has reached terminal velocity.
The terminal velocity is …
the fastest (highest speed) that the object can fall at.
Change in momentum =
force x time
The law of conservation of momentum says that …
momentum cannot be created or destroyed.
The law of conservation of momentum says that momentum cannot be created or destroyed.
So, if two objects collide, the sum of momentum before collision =
sum of momentum after the collision.
Change in momentum = mv - mu, where (letter meaning)
m is mass, u is the initial velocity of an object and v is the final velocity of an object.
What are the units of momentum?
Kgm/s
acceleration =
change in velocity ÷ time taken.
When a force acts on an object that is moving, or able to move, a ———————— happens.
change in momentum
mass × acceleration =
Force
(Using momentum) Force =
change in momentum ÷ change in time.
force is equal to the rate of …
change of momentum
If an object which has a lot of momentum is made to stop suddenly, then a ———- is required because of the change in momentum.
large force
Cars have safety features such as seat belts, air bags and crumple zones that absorb the …
kinetic energy transferred by collisions.
Cars have safety features such as seat belts, air bags and crumple zones that absorb the kinetic energy transferred by collisions.
These features reduce injuries to the people in the car by 1.
They increase the 2.
- absorbing energy when they change shape.
- time taken for the change in momentum to happen, reducing the forces involved.
What are the safety features of a car?
- seat belts
- crumple zones (front of the car)
- air bag
Using ideas about momentum, describe how a rocket is launched.
- The rocket starts at rest and has no momentum.
The rocket pushes the fuel out of the bottom of the rocket. - The fuel has gained momentum in the direction of the ground (earth).
- The conservation of momentum means that the rest of the rocket must gain momentum in the opposite direction. This propels (pushes) the rocket into the sky.
A moment is …
the turning effect of a force around a fixed point.
—————- is a good example for demonstrating how turning effects work.
Balancing on a see-saw
Balancing on a see-saw is a good example for demonstrating how turning effects work.
To balance the weight of a heavier person, a lighter person must …
sit further away from the pivot.
Doors open more easily if we press (exert force) far away from the hinge, rather than next to the hinge.
Pushing further away from the hinge (fixed point) means the moment is …
larger
The Moment (measured in Nm) is equal to the …
Force (measured in Newtons) multiplied by the perpendicular distance from pivot (measured in metres).
For an object to be in equilibrium in linear motion:
- There must be no resultant force acting on the object.
- It must be stationary or travelling at a constant speed in a straight line.
For an object to be in equilibrium in circular motion:
- The sum of the clockwise moments must be equal to the sum of the anti-clockwise moments acting on the object.
- This means that the object is not rotating or rotates at a constant speed.
Where is a turning effect larger?
As far away from the pivot as posssible.
For an object to be in equilibrium, it must be either …
stationary or moving at a constant speed in a straight line.
An object moving at a constant speed in a circle (circular motion) is —————- direction.
constantly changing
The resultant force always acts towards the ———— of the circle.
centre
The resultant force always acts towards the centre of the circle.
When on a roundabout, you have to …
pull yourself towards the middle to stop yourself falling off.
The resultant force always acts towards the centre of the circle.
When on a roundabout, you have to pull yourself towards the middle to stop yourself falling off.
Therefore, the object is accelerating towards the …
centre of the circle.
We use levers and gears to …
transmit (send) the rotational effect of a force from one place to another.
force.
Moment = force x distance, so using a lever means we need to …
use less force to get the same moment.
Gears are circular discs with ‘———’ around their edges.
teeth
Gears are circular discs with ‘teeth’ around their edges.
Their teeth interlock. So if we turn one gear, …
another turns in the opposite direction.
A set of gears can transmit (send) the …
rotational effect of a force from one place to another.
We can use ————— gears to change the moment of the force.
different sized
We can use different sized gears to change the moment of the force.
For example, if we send a force to a larger gear, there will be a …
bigger moment.
We can use different sized gears to change the moment of the force.
For example, if we send a force to a larger gear, there will be a bigger moment.
This is because the distance to the pivot is …
greater
What are the two ways of transmitting rational effects?
- lever
- gear
We use levers and gears to transmit (send) the ————- effect of a force from one place to another.
rotational
Stopping distance is the …
distance it takes a car to stop in an emergency (i.e. when the car is braking suddenly).
Stopping distance =
thinking distance + braking distance.
The time it takes for —————— is their reaction time.
a driver to react to a situation
The time it takes for a driver to react to a situation is their reaction time.
During this reaction time, the car …
carries on moving.
The thinking distance is the distance travelled between when the …
driver realises they need to brake and when they apply the brakes.
For a car travelling at ——-, a typical stopping distance is 12m.
20mph
For a car travelling at 20mph, a typical stopping distance is …
12m
For a car travelling at 50mph, a typical stopping distance is …
53m
For a car travelling at ——, a typical stopping distance is 53m.
50mph
For a car travelling at ——, a typical stopping distance is 96m.
70mph
For a car travelling at 70mph, a typical stopping distance is …
96m
What is the name of the distance travelled between when the driver realises they need to brake and when they apply the brakes?
Thinking distance
Several factors affect thinking distance. Some examples are:
- Tiredness
- Drugs or alcohol
- Distractions
If a car’s brakes or tyres are in ———- condition, then the braking distance will increase.
poor
——— (environmental) conditions will increase the braking distance.
Wet or icy
The ——— a car is travelling, the further it will travel before it comes to a stop.
faster
Stopping distance is the …
distance it takes a car to stop in an emergency (i.e. when the car is braking suddenly).
What happens when you press the breaks of a car?
When we push the brake pedal, brake pads are pressed onto the wheels.
This contact causes friction. This causes work to be done.
The work done between the brakes and the wheels converts (changes) energy from kinetic energy in the wheels to thermal energy in the brakes.
The temperature of the brakes then increases.
The greater the speed of a vehicle, the ———- the braking force needed to stop the vehicle before a certain distance.
greater
The greater the mass of the vehicle, the ———— the braking force needed to stop the vehicle. This means that more work needs to be done on the brakes to stop the car.
greater
The greater the mass of the vehicle, the greater the braking force needed to stop the vehicle. This means that —- needs to be done on the brakes to stop the car.
more work
For the same work done, the stopping distance will decrease if the force (grip) between the road and the vehicle …
increases
When a car comes to a stop, the work done by the brakes must equal the …
initial kinetic energy of the car.
Force x displacement
0.5 x mass x velocity 2
The greater the braking force, the ——— the deceleration of the vehicle.
greater
When a typical family car suddenly is stopped by a crash, an even ———- force is applied to the passengers than a emergency stop.
greater
When a typical family car decelerates at a set of traffic lights, only a ——— force is exerted on (applied to) the passengers.
small
When a typical family car decelerates at a set of traffic lights, only a small force is exerted on (applied to) the passengers.
This is because the …
deceleration happens over a long period of time.
When a typical family car decelerates at a set of traffic lights, only a small force is exerted on (applied to) the passengers.
This is because the deceleration happens over a long period of time.
The force should ———— to harm the passengers.
not be enough
When a typical family car suddenly stops on the road to avoid a collision, a ——— force is exerted on (applied to) the passengers.
greater
When a typical family car suddenly stops on the road to avoid a collision, a greater force is exerted on (applied to) the passengers.
This is because the …
deceleration happens over a shorter period of time.
Large ————- can cause the brakes to overheat and/or the car to skid.
decelerations
In fluids (liquids or gases), the particles ——— with the walls of their container.
collide
In fluids (liquids or gases), the particles collide with the walls of their container.
The particle exerts a …
force on the container and the container exerts a force on the particle.
The force exerted on the surface in contact with the fluid particle will be at the ———- to the surface (at right angles).
normal
The force exerted on the surface in contact with the fluid particle will be at the normal to the surface (——————-).
at right angles
pressure × area =
Force
Atmospheric pressure is the …
force per unit area created by the weight of the air (particles) in the atmosphere.
At the top of mountains, atmospheric pressure is ——- because there is less air (fewer particles) pressing down on the mountain.
lower
At the top of mountains, atmospheric pressure is lower because …
there is less air (fewer particles) pressing down on the mountain.
At the top of mountains, atmospheric pressure is lower because there is less air (fewer particles) pressing down on the mountain.
Air is lighter than water, but it still …
exerts pressure on the things beneath it.
When we move quickly up into the Earth’s atmosphere on a plane, your ears pop because of the …
drop in atmospheric (air) pressure.
We feel the weight of the atmosphere (on earth) as a pressure of:
100 kilo Pascals (100 kPa)
As you dive deeper into a swimming pool, there is ———- water (and weight) on top of you.
more
As you dive deeper into a swimming pool, there is more water (and weight) on top of you. This extra weight exerts a …
larger force (and higher pressure) on your body.
If the object’s weight is equal to the upthrust, then the …
forces balance and the object will float in the liquid.
The pressure beneath a liquid’s surface =
density of fluid x gravitational field strength x depth.
Pressure is measured in …
pascals (Pa).
Density of fluid is measured in …
g/cm3.
Depth is also equal to …
the height of the column of water above you.
A partially submerged object (an object that’s not fully in a liquid) will experience greater pressure on the bottom surface than on the top surface. This creates a …
resultant force upwards.
A partially submerged object (an object that’s not fully in a liquid) will experience greater pressure on the bottom surface than on the top surface. This creates a resultant force upwards. We call this force …
upthrust
The upthrust that acts on an object is equal to the …
weight of the liquid that has been forced away (displaced) by that object.
If the object’s weight is greater than the upthrust, then the object will …
sink
Submarines use the balance between ———- to control their depth in water.
upthrust and weight
When a submarine wants to come up to the surface, it fills its tanks with …
compressed air to reduce its weight.
When a submarine wants to come up to the surface, it fills its tanks with compressed air to reduce its weight.
Weight becomes ——— than upthrust so the submarine rises.
less
When a submarine wants to sink, it fills its tanks with …
water to increase its weight.
When a submarine wants to sink, it fills its tanks with water to increase its weight.
This means the submarine’s weight is ——- than the upthrust and it sinks.
greater
The pressure difference is equal to the …
density of fluid multiplied by the gravitational field strength multiplied by the change in depth.
What do we call the point through which an object’s weight appears to act?
Centre of gravity
