Forces and acceleration Flashcards
What is the resultant force?
The overall force on an object
In most situations there are … acting on an object.
at least two forces
What do all the forces acting on an object decide?
The motion of the object, e.g accelerate or stay still, or stay at a steady speed
If you have a number of forces all acting on the same point you can…
Turn it into a single force, as long as it has the same effect on the object’s motion.
What is the overall force called?
Resultant force
What does 10N of gravity pushing a teapot onto a table cause?
10N of reaction force, the surface pushing it up, to make the teapot balance and not accelerate towards the earth.
What does a resultant force mean?
If there is a resultant force acting…
A change in velocity
The object change its state of rest or motion, causing a change in the object’s velocity.
An object needs a force to…
If the resultant force = 0 the object will…
Start moving
Remain stationary
No resultant force =
No change in velocity, it’ll just keep moving at the same velocity
If x is traveling at a constant velocity, all the forces must be…
To keep going at a constant speed there must be what kind of resultant force?
all the forces must be balanced
there must be a 0 resultant force,
A resultant force =
If there is a non-zero resultant force…
A non-zero resultant force will always…
Steady speed when…
Acceleration
Then the object will accelerate in the direction of the force
..produce acceleration
… there is 0 resultant force
What are the five forms of acceleration?
Start, stop, speed up, slow down, change direction
You get a steady speed when there is ….
0 resultant force
A non- zero resultant force always produces an …
What is the formula for this?
acceleration
F=ma
Force, resultant (N) = mass (kg) X acceleration (m/s squared)
Reaction forces are … and ….
equal and opposite
Describe the forces exerted when two objects interact?
When two objects interact the forces exerted on each other are equal and opposite
Equal and opposite reactions mean that when you push a trolley it will ….. against you ……..
When you stop pushing …..
So when you push something …. …… back with the …. amount of force
…push back against you just as hard
… so does the trolley
… it pushes back with the same amount of force
Friction always …
.. slows things down
What will happen to an object when its pushing force stops, in relation to friction?
It will slow down and stop due to friction
Friction will always act in the …. direction to the movement
opposite
To travel at a steady speed the driving force needs to …. the frictional forces.
balance
Where do you get friction (2) ?
When two surfaces come into contact
When an object passes through a fluid
What is a fluid?
Air or liquid
Most resistive forces are caused by what?
How can you reduce these forces?
Air resistance or ‘drag’
Make the object streamlined
What is the opposite object to a streamlined one?
A parachute, designed to have the biggest surface area to make as much drag as possible to slow the person down.
Drag increases when….
speed increases
Frictional forces in fluids always…..
increase with speed.
A car had much more friction to …. ……. when travelling at 70mph compared to 30.
So at 70mph the engine has to ….. …… ….. to maintain a steady speed.
work against
wok much harder
Objects falling through fluids eventually reach a ….
reach a terminal velocity
1.What happens when a parachutists first set off?
Refer to gravity, friction, and overall current speed.
2.As their speed increases…..
3. What happens to the frictional force in relation to the acceleration?
4. What is this called?
- The force of gravity is much more than the frictional force slowing them down , so they accelerate.
- … friction builds up.
- As the friction builds up and slows them down it reduces the acceleration until the frictional force is = to the accelerating force, so it won’t accelerate any more.
- It will have reached terminal velocity and will fall at a steady speed
What does the velocity/time graph look like for a parachutists falling who then reaches terminal velocity?
A gradual slope upward from left to right, like a hill cut in half (the opposite to exponential growth) then it levels off at the top and flat lines, not getting any steeper or shallower.
Terminal velocity depends on what two things?
Shape and area
What is the accelerating force on all objects?
It would make all objects fall at the same rate if not for….
What does this mean for a hammer and feather on the moon?
Gravity
Air resistance
As there’s no air there is no air resistance so they fall at the same rate due to gravity
Air resistance on earth causes things to fall at ….
different speeds
The terminal velocity of an object is determined by its…
The frictional force depends on its ….
drag in comparison to its weight.
shape and area
Describe the fall of a skydiver….
- Before he opens his parachute he has… (friction, equation?
- He reaches a terminal velocity of….
- But with his parachute open there is …
- What does this mean for his TVelocity? Why is this good for a parachutist?
- … a small surface area and a force of W=mg pulling him down
- 120mph
- …much more air resistance but still only the same gravitational force pulling him down, W=mg
- It comes down to about 15mph which is a safe speed to hit the ground at
