P4

Question 1

What is important about forces ?

Answer 1

• Forces always arise from an interaction between two objects
• the two forces in an interaction pair
• the forces are of equal size

opposit in direction

the two forces act on different objects

Question 2

What are the two kinds of interaction pairs?

Answer 2

1. two objects touch eachother
   - contrast forces
   - as soon as the objects seperate the forces stop
2. called action at adistance
   - magnetism
   - attracted when near magnets
   - forces act all the time
   - forces get weaker as the distance increases

Question 3

What are some examples of interaction pairs?

Answer 3

• Rocket
• push out hot gases
• rocket exerts dowward force o the gases
• gases exert an upward force on the rocket
  2. car wheel

Question 4

What cause the size of the friction?

Answer 4

• depends on external force
• up to a certain limit

limit determined by weight and roughness of the surface and the object

Question 5

What s frction and what causes it ?

Answer 5

• interaction between two surfaces
• slide against eachother

friction acts in the opposite direction of the force you exert

Cause

• caused by roughness of the sliding surfaces
• bumps on two surfaces don’t fit- resistance

Question 6

What is the sum of forces acting on an object?

Answer 6

-resultant force

Question 7

How can a table exert a force?

Answer 7

• table with a tennis ball is like a school bag on a cushion
• there is a downward force from the ball on the table
• ther is an upward force from the table on the ball

Question 8

How does freefall work?

Answer 8

• ball dropped
• increaes it speed until it reaches terminal velocity
• falls at a constant speed

Question 9

What is the difference between displacement and distance?

Answer 9

• distance is the length of the route alon a path
• displacment is the shortest distance from a to b

Question 10

What is the formula for average speed and acceleration?

Answer 10

Distance(m)= speed(m/s) times time taken (s)

acceleration= change of speed divided by time taken for the change (s)

Question 11

How do you find speed on a distance time graph?

Answer 11

find the gradient

Question 12

What is a displacement time graph?

Answer 12

show the path of an object that moves in a straight line

Question 13

What is special about a velocity time graph?

Answer 13

• can show direction and speed

Question 14

What is the formula for momentum?

Answer 14

Question 15

What is important to know about the change of momentum in an interaction pair?

Answer 15

1. the change in momentum is the same
2. the resultant force acting on the objects is the same
3. the time for which the force acts is the same

Question 16

What is the formula for change in momentum?

Answer 16

Question 17

What are the safety precautions in cars?

Answer 17

-crumple zone

increases time the force acts on the car

• less force on you
• seat belts, air bags

make changes momentum take longer

less force

Question 18

What are Newtons three laws of motion?

Answer 18

1. If the resultant force acting on an object is zero. the momentum of the object does not change
2. If the ther is a resultant force acting on an object , the momentum of the object will change and the size of the change of momentum is equalto the resultant frce times the time taken for the force to act. the change is in the same direction as the resultant force
3. When two objects interact, each experience ` force. The two forces are equal in size, but opposite in direction.

these laws apply all objects and every situation apart from objects at the subatomic level or moving at the speed od light.

Question 19

What is the formula for work done, kinectic energy and gravitational potential energy?

Answer 19

Gravitational potentail energy(j)=weight(N) times vertical height

Question 20

What is the relationship between GPE and kinectic energy?

Answer 20

decrease in GPE=increase in kinectic energy