P4 Explaining Motion Flashcards
What is instantaneous speed?
The speed at a particular moment in time
What is the equation to find speed?
Speed(m/s) =distance travelled(m)/ time taken(s)
What Is displacement?
Distance traveled away from start point in a straight line.
Example of displacement:
E.g. When you run around a race track, the distance travelled is 400 but the displacement is 0.
What is velocity?
The velocity of an object is its speed in a certain direction.
What is the equation to find velocity?
Average velocity= displacement(m)/time taken(s)
How do you find the speed and object is travelling on a distance time graph?
The steeper the gradient of the line the faster the speed. Gradient = distance/time (speed)
What does a curved line on a distance time graph mean?
A curved line means the speed is changing. A steeper line means the vehicle is getting faster.
what does a displacement time graph show?
A displacement time graph shows the speed and distance something is moving from a certain point in a certain direction.
Definition of acceleration;
Rate at which the speed of an object increased
Equation for acceleration.
Acceleration(m/s*)=
change in speed(m/s) / time taken(s)
*= squared
Acceleration is defined as a rate of change in velocity. What is the equation for this?
Acceleration =
Change in velocity/time taken
What is the instantaneous speed of a vehicle in a certain direction?
Instantaneous velocity
In a speed time graph there is a horizontal line at along the x-axis. Usually this would mean the object is…
Stationary
What does a velocity-time graph show?
The direction I’m which an object is travelling.
What is meant by a positive and negative velocity.
Positive=object travels in certain direction
Negative=object moves in opposite direction.
The gradient of a velocity time graph is equal to…
Acceleration.
A cyclist rides around a velodrome track. When he sets off he takes 1 minutes to reach a top speed of 14m/s. Then he cycles 10 laps round the oval track at a constant speed. Calculate the cyclists initial acceleration,and explain why he continues to accelerate after that.
Ask someone or check in revision guide
When a ship floats on water, the upthrust (buoyancy) pushes on the ship and the ship pushes down on the water. What is this an example of?
Interaction pair.
What is a reaction force?
A force that is equal and opposite to the five that has been applied.
Describe an interaction pair.
Two forces that are equal in size, opposite In direction and act on different objects.
What happens with an interaction pair when you push harder in one direction?
The reaction force increases then there is an imbalance and the force applied overcomes the reaction force and you accelerate.
Forces are vector quantities. I.e…
And can be shown as a narrow on a scale diagram to show…
They have magnitude(size) and a direction. This can be shown by
Describe the interaction pair that makes a jet move.
Jets push gas out of back of engine. Gads pushes back on engine with equal and opposite force which propelled the jet forward
The size of the friction force depends on… (2 points)
- Roughness of surface
- How hard the surfaces are pushed together (heavier object=more friction)
What is ‘limiting friction’?
When friction has reached a maximum value and the force applied can no longer be equaled by an opposite reaction.
As you increase the applied force the friction will increase in an equal opposite reaction eventually the friction reaches a maximum value And the object will start to move. What is this called?
Limiting friction
What is the overall force action on an object called?
Resultant force
What is the resultant force
The overall force acting on an object
When an object can speed up, slow down or change direction, it’s forces are…
Unbalanced
When the forces are balance and acceleration and resultant force are equal to zero, what will the object do?
Carry on moving in the same direction at a constant speed.
The constant, maximum speed reached by a falling object is know an…
Terminal velocity
Give examples of car safety devices that are designed to increase the impact time, thus reducing the force in a collision.
Air bags, crumple zone, seat belts,crash helmets
What does, force x distance moved in the direction of force =?
Work done
1 joule of work will lift a weight of 1 Newton a distance of 1 metre. This work is transferred to… Of the object.
Gravitational potential energy.
Weight x vertical height difference =
Change in gravitational potential energy.
Give examples of car safety devices that are designed to increase the impact time, thus reducing the force in a collision.
Air bags, crumple zone, seat belts,crash helmets
If you weight is 700N and you climb stairs a height of 3m what is your gain in GPE?
Weight x height = 700N x 3m = 2100J
When you increase an objects velocity you do work. The work is transferred to the moving object as …
Kinetic energy (KE)
The equation for momentum=
Mass(kg) x velocity
If a car of mass 800kg is moving at the speed of 12m/s. What is its KE?
KE = 1/2 x mass x velocity
1/2 x 800 x 12(squared) = 57600J
The energy of a moving object is its …
Kinetic energy.
Mass x velocity = …
Momentum
A resultant force will cause a change in momentum. What is the equation to find force?
Force = change in momentum / time taken
Force is equal to the rate of change of momentum.
On a displacement time graph a vehicle at its starting point is 0, when would the displacement be negative?
When the vehicle is behind its starting point.
Give and example of an interaction pair.
Rockets push out gas with a large force. The gas pushes back on the engine with and equal but opposite force. The rocket is pushed forward.
What is drag?
The upward force that’s slows down a falling object.
What makes drag increase?
The increased speed of an object.
And the increased surface area of an object.
Describe how the forces act on the flash when jumps of the top of a building to beat the speedster who is faster than him?
At first the gravitational pull is far greater than the drag. There are unequal forces so The flash increases in speed the drag also increases. The acceleration therefore decreases. Eventually the he reaches terminal velocity where the drag force is equal to the gravitational pull. This results in no resultant force and the acceleration is zero. The same thing happens to the speedster. They are falling at an equal rate. Allowing the flash to catch up with his opponent and beating him!!!
What does the size of a force depend on?
Faster(velocity) = larger force
Heavier(mass) = larger force
Duration of the impact(longer time to stop) = lower force.
What changes an objects momentum?
The total overall force on an object (resultant force) ✖️
the time for which it acts. (The longer the time before stoping = the smaller the force).
If a car has a mass of 1200kg and it crashes into a wall at the speed of 20m/s. What is its change in momentum?
The collision stops the car in the time of 1.5 seconds. What was the force?
Change in momentum = 1200 x 20 = 24000kg m/s
Force = 24000/ 1.5 = 16000N
What is work done?
The energy used by the movement of a force.
When work is done by and object. Energy is transferred from that object to something else.
How do you find work done? (Equation)
Work done = force (N) x distance moved in direction of force (m)
What changes an objects momentum?
The total overall force on an object (resultant force) ✖️
the time for which it acts. (The longer the time before stoping = the smaller the force).
If a car has a mass of 1200kg and it crashes into a wall at the speed of 20m/s. What is its change in momentum?
The collision stops the car in the time of 1.5 seconds. What was the force?
Change in momentum = 1200 x 20 = 24000kg m/s
Force = 24000/ 1.5 = 16000N
What is work done?
The energy used by the movement of a force.
When work is done by and object. Energy is transferred from that object to something else.
How do you find work done? (Equation)
Work done = force (N) x distance moved in direction of force (m)
Work done(j) = amount of…
Energy transferred(j)
Write the equation for gain in gravitational potential energy.
GPE = weight (N) x height difference(m)
1 joule of work = lift weight of 1 Newton = a distance of 1 meter
Equation for work done…
Work done = force x distance moved in direction of force.
When work is done by an object it transfers energy from the object to something else.
