Flashcards in Movement Y10 Deck (29)
What is speed?
Distance ÷ time
What is the difference between speed and velocity?
Velocity has a direction, speed does not
What is acceleration?
How fast an object changes its velocity
Acceleration = (velocity final - velocity initial) ÷ time
Measured in m/s^2
What is force?
Force = mass x acceleration
How does force relate to acceleration?
Force is proportional to acceleration
What is the acceleration of a rocket of mass 50kg and thrust 1200N?
Weight = 50 x 10 = 500N
Overall force = 1200-500 = 700N
Acceleration = 700 ÷ 50 = 14m/s^2
What is terminal velocity?
When acceleration and overall force are both 0
What are the three stages of an object falling?
1) object accelerates downwards due to weight. No drag ∴ overall force downwards
2) as object gains speed, air resistance increases, but weight stays same, so overall force decreases. Acceleration also decreases
3) eventually drag balanced weight, so no overall force or acceleration. Now it has reached terminal velocity.
How can you increase terminal velocity?
Increase the force to increase the acceleration
Make it more streamlined to decease the air resistance
What is thinking time and what can affect it?
Time to react to what you see. Tiredness, visibility, drug/alcohol use, concentration
What is stopping time and what can affect it?
Time between putting foot in break and stopping. Tyres, conditions, breaks, ground
In a distance time graph, what does the gradient represent?
In a velocity time graph, how do you find the distance?
How do you work out a moment?
Moment(Nm/Ncm) = force x distance
If a person moves from left to right on a bridge, what will happen and why?
The CM will increase, therefore Rr must increase. To do this, Rr's force must increase.
What is Hooke's law?
Force is proportional to extension, as long as elastic limit has not been reached
What are elastic and plastic behaviour?
Elastic = when force removed spring goes back to original length
Plastic = when force removed spring stays a bit stretched
What does a spring's graph tell you?
Straight line through origin ∴ force proportional to extension
F = K x E
What is the spring constant in 2x springs?
In series: 0.5K
In parallel: 2K
What is a force? (newton's 1st law)
That which causes an object to accelerate
What is Newton's third law?
• for every action there is an equal but opposite reaction
∴ for a force to exist there must be two objects. The size of the force on each object will be the same, but they don't cancel out, as act on different objects
E.g. When you jump up the earth has a downward gravitational pull on you of 500N, but you have an upward gravitational pull on the earth of 500N
What is momentum? Is it vector/scalar?
• momentum = mass x velocity
• measured in kgm/s
• vector ∴ direction imp
• you may need to say the direction of the momentum
What is the principle of conservation of momentum?
Total momentum before an action=total momentum after reaction as long as no external forces, e.g. Friction etc.
Wat do you do in explosion problems?
• total m to left = total m to right
• ∴ work out m on one side, then that will be m on other. Therefore you can solve for 1 unknown
What do you do in collision problems?
Subtract the momentum of one object from the momentum of the other object to find the overall m. (remember direction v important)
Then using the PoCoM:
Total mass x velocity = the m you worked out before
Solve for whatever you need to know
What is newton's 2nd law?
Force = change in m /time
How does newton's 2nd law have an effect on car safety/crashes/jumping?
In these cases you want smallest possible force, to avoid injury ∴ as we can't change the initial/final momentum, what we, use do is increase the time taken
We do this by bending knees on impact/crumple zones in cars/airbags
How can changing forces affect speed and direction?
• upwards and downwards forces are balanced
• accelerating: forwards force greater than backwards force
• decelerating: backwards force (drag/friction) greater than forwards force
• direction will travel in whatever direction the force is greatest