Our Dynamic Universe Flashcards
Key area: Equations and graphs:
If the line in a velocity-time graph crosses the x-axis, what does this represent?
The object changes direction.
Key area: Equations and graphs:
Why does the velocity-time graph of a bouncing ball diminish to zero as the ball bounces?
Energy is transferred to other forms during its journey.
Key area: Equations and graphs:
In a displacement-time graph, what does the gradient represent?
Velocity
Key area: Equations and graphs:
In a velocity-time graph, what does the gradient represent?
Acceleration
Key area: Equations and graphs:
When considering velocity or acceleration in opposite directions (left/right, up/down), what must be given to the values?
Values must be assigned a positive or negative value e.g. down (-), up (+) or left (-), right (+) The + and - directions must be kept consistent throughout the problem.
Key area: Forces, energy and power
When considering the acceleration of a rocket, what forces must be taken into consideration?
Thrust (upwards) Weight (downwards)
Key area: Forces, energy and power
What causes an object to reach its terminal velocity?
The forces become balanced, therefore the object cannot accelerate any more.
Key area: Forces, energy and power
What three things could cause the acceleration of a rocket headings towards space to increase?
Reducing mass due to consumption of fuel. Reducing air friction as the rocket moves further from the Earth’s surface. Reducing influence of gravity as the rocket moves away from Earth.
Key area: Forces, energy and power
If an object is struck with a diagonal path into the air, what must be done to analyse its motion?
The diagonal path must be resolved into horizontal and vertical components of the motion of that object.
Key area: Forces, energy and power
If an object has 200J of gravitational potential energy at the top of a slope and has 180J of kinetic energy once it has rolled down the slope, what has happened to the missing 20J?
Potential energy has been converted into forms other than kinetic, such as heat and sound energy.
Key area: Forces, energy and power
Define friction
Friction is a force which opposes the motion of an object.
Key area: Forces, energy and power
A block is being pulled along a surface by a force. There is friction between the block and the surface. What must be done before the motion of the block is analysed further?
The frictional force must be subtracted from the pulling force to find the resultant force.
Key area: Collisions, explosions and impulse
State the law of momentum
For a collision occurring between object 1 and object 2, the total momentum of the two objects before the collision is equal to the total momentum of the two objects after the collision in the absence of any external forces.
Key area: Collisions, explosions and impulse
In what situation is a collision elastic?
Where the total kinetic energy after the collision is equal to the total kinetic energy before.
Key area: Collisions, explosions and impulse
In what situation is a collision in inelastic?
Where the total kinetic energy after the collision is less than the total kinetic energy before.
Key area: Collisions, explosions and impulse
Using the relationship Ft = mv - mu to help explain, why does a crumple zone or airbag limit the injury to the occupant of a car?
The momentum of a car’s occupant will reduce significantly during a collision. Rearranging the equation for F shows that the longer the collision, the less the average force on the person.
Key area: Collisions, explosions and impulse
If two balls of the same mass fall from the same height onto a force sensor, how would their force-time graphs compare if one was made of a solid material and the other was made of a flexible material?
The objects would have the same momentum before the collision as mass and speed are equal. On contact with the sensor, the force exerted by the flexible ball will be applied over a longer time. The graph of the hard ball would be tall and narrow, the graph of the softer ball would be short and wide but both would have the same area underneath them.
Key area: Gravitation
Explain how a satellite orbits a planet or star.
Satellites are in constant freefall under the influence of the gravity of the object they are orbiting. The satellites must have sufficient horizontal velocity for it to continue in orbit where its motion can be considered as a projectile path.
Key area: Gravitation
What can be said about the horizontal and vertical motion of a projectile?
Both horizontal and vertical motions are independent of each other.
Key area: Gravitation
According to Newton’s Universal Law of Gravitation, what two things influence the force between two objects.
1) The mass of the two objects. 2) The distance between the two objects.
Key area: Special Relativity
What can be said about the speed of light, regardless of a person’s frame of reference?
The speed of light is constant.
Key area: Special Relativity
How does the measurement of time differ for a moving observer compared to a stationary observer?
Measurements of time for a moving observer are different compared to those for a stationary observer, giving rise to time dilation.
Key area: Special Relativity
For a stationary observer how does the length of an object moving at speed compare to the length of the object at rest?
The moving object appears to be shorter.
Key area: The Expanding Universe
As an object moves away from a stationary observer, what does this do to: a) the apparent colour of light it emits? b) any sound it may make?
a) Light from an object moving away will shift towards the red end of the spectrum (red shift). b) Sound being emitted by an object moving away from an observer will sound lower in pitch than the sound the object is emitting.
