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Roof knocking

Roof knocking is a physics topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Roof knocking rather than just read about it. In short: Roof knocking (Hebrew: הקש בגג) or "knock on the roof" is a term used by the Israel Defense Forces (IDF) to describe its practice of dropping low-yield devices on the roofs of targeted civilian homes in the occupied Palestinian territories as a prior warning of imminent bombing attacks to give the inhabitants time to flee the attack. The practice was employed by the IDF during the 2008–2009 Gaza War, the 2012 Gaza W…

Key takeaways

  • Roof knocking belongs to physics; place it in that map before memorising details.
  • Learn the definition first, then one example that makes the definition concrete.
  • Connect Roof knocking to a quantity you can measure, compute or draw — that is where exam questions come from.
  • Reproduce the core statement of Roof knocking from memory before moving on to harder problems.

Reference excerpt

Roof knocking (Hebrew: הקש בגג) or "knock on the roof" is a term used by the Israel Defense Forces (IDF) to describe its practice of dropping low-yield devices on the roofs of targeted civilian homes in the occupied Palestinian territories as a prior warning of imminent bombing attacks to give the inhabitants time to flee the attack. The practice was employed by the IDF during the 2008–2009 Gaza War, the 2012 Gaza War, the 2014 Gaza War, and the since 2023 ongoing Gaza War to attack a variety of targets. The application of roof knocking is often argued to only have legal reasons rather than the intention to reduce civilian casualties. The impact of the smaller device often puts the civilian population in a state of shock, making them unable to flee the larger attack which often follows only 45 to 180 seconds later. According to the IDF, this period must be very short as otherwise targeted weapons could be removed, however, in practice the period proves to be too short for civilians to flee. Civilian casualties after a "knock on the roof" are often considered human shields by Israel, without differentiating between voluntary and involuntary human shields.

History As early as 2006 the IDF had the practice of warning the inhabitants of a building that was about to be attacked. Roof knocking was used during the 2008–2009 Gaza War, the 2012 Israeli operation in the Gaza Strip, and the 2014 Gaza War. In the six months prior to its use, Israel collected data on Hamas members, which they used to issue warnings. Typically, Israeli intelligence officers and Shin Bet security servicemen contacted residents of a building in which they suspected storage of military assets and told them that they had 10–15 minutes to flee the attack, although in some cases the delay has been as little as five minutes.

Adoption by the U.S. military In 2016, it was published that the US military adopted the Israeli battlefield tactic in its war against Islamic State. It was used in an attack against an ISIS storage facility in Mosul, Iraq. As women and children lived in the house, a Hellfire missile was initially shot at the roof as a warning.

Gaza war During the Gaza war, CNN reported that many people in Gaza said the IDF had abandoned the "roof knocking" policy. In October 2023, a senior Israeli official stated that the practice would no longer be the norm and would only be used under certain circumstances. An IDF officer told The New York Times that instead of the "roof knocking" policy, Israel is issuing mass evacuation orders and leaflets stating that "anyone who is near Hamas fighters will put their lives in danger."

Defiance In some cases, residents who were warned about an impending bombing climbed up voluntarily to their roofs to show they would not leave. When Nizar Rayan, a top Hamas military commander, was warned but did not leave his home, he and his family of 15 were killed in the subsequent bombing. When faced with similar situations, IDF commanders have either bombed, called off the bombing or launched a warning missile at empty areas of the roof, in order to frighten the people gathered on the roof into leaving the building. The New York Times stated that according to Israel, Hamas asked residents to stand on the roofs of buildings to dissuade Israeli pilots from attacking their homes. A NATO report confirmed the practice, describing it as an example of lawfare. However, Amnesty International argued that Hamas' purported call may have been "motivated by a desire to avoid further panic" among civilians, considering both the lack of shelters in Gaza and the fact that some civilians who heeded the IDF's warnings had been casualties of Israeli attacks. Many reporters, including from the BBC, The Independent, and The Guardian have said that they have found no evidence of Hamas forcing Palestinians to stay and become unwilling human shields.

Reactions The practice has been controversial, as many human rights and news organizations have shown that 'roof knocks' have killed and injured civilians. In July 2014, Amnesty International called for a United Nations investigation into what it alleged were war crimes committed by Israeli fighters, and Philip Luther, Middle East and North Africa Programme Director for the organization, condemned the practice. The spokesperson for Gaza Health Ministry indicated that the same missiles used to give warnings are also used in assassinations, resulting in dozens of casualties and deaths where "remains were scattered, making it impossible to identify them immediately". The Goldstone Report commented that civilians inside their homes "cannot be expected to know whether a small explosion is a warning of an impending attack or part of an actual attack". It stated that the practice is not an effective advance warning, and is instead likely to "cause terror and confuse the affected civilians". The Israeli Government stated "While these warnings, could not eliminate all harm to civilians, they were frequently effective," and that aerial video surveillance by IDF forces showed civilians departing from targeted areas prior to an attack as a direct result of the warnings. According to the Israeli army, striking homes suspected of storing weapons, when sufficient warning is given to the residents, falls within the boundaries of international law and is legitimate. In November 2014, the most senior US military official, General Martin Dempsey, cited "roof knocking" as an example where Israel "did some extraordinary things to limit civilian casualties" during the 2014 Gaza War. Salah Abdul Ati, the directory of the Palestinian Independent Commission for Human Rights in Gaza, described the "policy of destroying homes" a war crime and accused Israel of attempting to circumvent international law to avoid accountability. Marouf Hasian Jr., a professor of communication at the University of Utah, describes the talk of the "beneficent usage" of "knock on roof" tactics as one that "plays well in front of American or Israeli audiences who feel that older Geneva Convention rules are too 'quaint' and too solicitous of the rights of civilians who may be aiding and abetting terrorist, but it infuriates critics who argue that satellite surveillance is being used in discriminatory systems that assume that homes of police officers or Hamas political or military leaders can be "precisely" targeted to minimize collateral damage".

… excerpt ends here. Continue reading the full article.

Worked examples

Example 1 — a first encounter with Roof knocking

Start with the simplest possible case. Write down what Roof knocking claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In physics, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Roof knocking before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Roof knocking ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Roof knocking

In research
Roof knocking appears in physics research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry
Engineering practice reuses Roof knocking in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom
Roof knocking is common in secondary-school and first-year university syllabi. It links to neighbouring topics 2014 Gaza War, Aerial warfare tactics, Civilians in war, so understanding it makes those chapters shorter.
In everyday life
Look for Roof knocking outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Roof knocking in 20 minutes

  1. Read the reference excerpt below once, without taking notes.
  2. Close the page and write down what Roof knocking means in your own words.
  3. Compare your version with the excerpt and mark what you missed.
  4. Work through the three examples above with pen and paper.
  5. Explain Roof knocking out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Roof knocking in simple terms?

Roof knocking (Hebrew: הקש בגג) or "knock on the roof" is a term used by the Israel Defense Forces (IDF) to describe its practice of dropping low-yield devices on the roofs of targeted civilian homes in the occupied Palestinian territories as a prior warning of imminent bombing attacks to give the…

Why does Roof knocking matter?

Because it connects several physics ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Roof knocking?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Roof knocking.

Tags

  • 2014 Gaza War
  • Aerial warfare tactics
  • Civilians in war
  • Destruction of buildings
  • Gaza War (2008–2009)
  • International law
  • Israel Defense Forces
  • Phrases related to the Israeli-Palestinian conflict
  • Residential building bombings in Palestine
  • Roofs

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