Term 1 Flashcards
Newton’s First Law
If the resultant force acting on an object is zero:
- If the object is stationary, it will remain stationary
- If the object is moving, it will continue to move at the same speed in the same direction
Newton’s Third Law
When 2 objects interact, the forces they exert on each other are equal and opposite i.e. weight, a tennis ball pulls on the Earth and the Earth pulls on the ball with equal force
Example of a Newton 3 pair
A ball on a table, the ball pushes on the table and the table pushes on the ball with equal and opposite force
When might Newton’s 3rd law apply?(4)
-There are two ‘objects’
-The forces are of the same type
-The forces are equal in magnitude (also applies to balanced forces)
-The forces are opposite in direction (also applies to balanced forces)
Inertial mass
A measure of how difficult it is to change the velocity of an object
Newton’s Second Law
Resultant force = mass x acceleration
F = ma
Acceleration
Rate of change in velocity, change in velocity per second
Acceleration is…
-Proportional to the resultant force acting on an object
-Inversely proportional to the mass of an object
Acceleration formula
a = v-u/t
Uniform motion
Acceleration is constant
Symbols for motion(4)
s - displacement in m
u - initial velocity in m/s
v - final velocity in m/s
a - acceleration in m/s squared
Initial velocity
Speed of an object before acceleration/deceleration
Final velocity
Speed of an object after acceleration/deceleration
When an object is accelerating uniformly…
v squared - u squared = 2as
When there is no air resistance, gravity gives a falling object an acceleration of…
9.8m/s squared
When a ball is thrown upwards…
it decelerates and acceleration is then -9.8m/s squared
What do velocity-time graphs show
How the velocity of a moving object changes over time
When dealing with non-constant acceleration, what acronym do you use?
F(orces)
R(esultant force)
A(cceleration)
V(elocity)
How do the forces acting on a skydiver change from when he jumps out of the plane to before he deploys the parachute(5)?
-As soon as the skydiver jumps out of the plane, the only force acting on him is the downward force of weight (this is due to gravity, this force will never change throughout the scenario)
-This means his resultant force is his weight (ma = mg, mass cancels out so the gravitational field strength = acceleration), so he is accelerating at 9.8m/s squared
-As the skydiver falls, his velocity increases, and therefore the amount of the upward force of drag he experiences increases
-This drag reduces his resultant force (Resultant force = weight
- drag), therefore reducing his acceleration
-At a certain point, the drag that was increasing will be equal to the weight, making his resultant force zero, and with Newton’s first law that means his acceleration is zero and he has reached terminal velocity and is now travelling at constant speed
How do the forces acting on a skydiver change from when he jumps out of the plane to after he deploys the parachute?
-The skydiver then opens their parachute, causing the air resistance to massively increase and making the drag greater than the weight. This causes the skydiver’s to decelerate and his velocity decreases
- However, since the velocity has decreased, his air resistance will also decrease and eventually the forces will balance again and he will once again achieve terminal velocity, this time at a lower speed
Terminal velocity
The maximum speed of the object, reached when the forces moving the object are balanced with the frictional forces i.e. air resistance
Stopping distance
The distance needed for a vehicle given speed to stop
Stopping distance is…
Thinking distance + Braking distance
Thinking distance
Distance the vehicle travels during the driver’s reaction time
