☰ خطة العام · العلوم (بالإنجليزية)

Motion, position and forces

الأسبوع 10 · المحور الثاني «المادة والطاقة»، الوحدة الثانية «الحركة»: ابدأ، المفهوم 2.1 «الحركة والتوقف» (أ): القوى التي تحرك الأجسام · 3 دروس
3

Forces that start motion

Discovery Education Science P4: Term 1, Unit 2, pp. 116–129
GoalDescribe forces as pushes and pulls, including gravity, and show several forces acting on one object.
New words
force · a push or a pullgravity · the pull of the Earth that pulls things toward its centrepush · a force that moves something away from you
Explanation

A force is a push or a pull. Forces can start something moving, speed it up, slow it down, change its direction, or stop it. You push a door to open it and pull a drawer. Gravity is a force too: it pulls everything toward the centre of the Earth. That is why a ball you drop falls down, and why things have weight. Often more than one force acts on an object at the same time. A book on a table has gravity pulling it down and the table pushing it up. If two people push a heavy box in the same direction, the forces add. If they push in opposite directions, they work against each other. We draw a force as an arrow: it points the way the force acts, and a longer arrow means a bigger force.

PushPull
Worked examples
gravitytable pushes up
A book rests on a table. Gravity pulls it down and the table pushes it up. Two forces act on one object.
Karim and Nour push together
Karim and Nour both push a box to the right. Their pushes add up, so the box moves more easily than if one child pushed alone.
kitewind pushesstring pulls
A kite is pulled by the string toward the child, and the wind pushes it away. Gravity pulls it down at the same time. A kite has several forces acting on it.
Class activity

Push-pull hunt. With a grown-up, walk through your home and find six pushes and pulls (a door, a drawer, a tap, a ball, a curtain, a bag). Write each in a table with two columns: Push, Pull. For one of them, draw a force arrow and show which way it points. Find one example of gravity (something falls or stays on the table).

Practice
1
Is opening a drawer a push or a pull?
2
Which force pulls things toward the centre of the Earth?
3
Two forces act on the cup on the table. Say their directions.
??
4
In a force picture, what does a longer arrow mean?